Effects of body condition score and nutrition in lactation on twin-bearing ewe and lamb performance to weaning

Abstract

This study investigated the effect of feeding and body condition during late pregnancy and lactation on both ewe and lamb performance until weaning. On day 141 of pregnancy, ewes with a body condition score (BCS) of 2.0, 2.5 or 3.0 were allocated a ‘Low’, ‘Intermediate’ or ‘High’ feeding treatment until weaning at day 79 of lactation. Feeding treatments had no effect on lamb live weight at birth, summit metabolic rate or indices of colostrum intake (P > 0.05). At weaning, lambs born to the High treatment were heavier than the Intermediate treatment, which were heavier than the Low treatment (P < 0.05). Lambs reared by ewes with a BCS of 2.0 were lighter during the lactation period than lambs whose dam had a BCS of 2.5 or 3.0 (P < 0.05). In addition, lambs reared by ewes with a BCS of 2.0 had greater summit metabolic rates and greater survival to weaning than those reared by BCS 3.0 (P < 0.05) but not BCS 2.5 (P > 0.05). There was, however, no effect of feeding treatment on lamb survival to weaning. These results indicate that, within these BCS, benefits could be gained from greater BCS in late pregnancy across all feeding treatments.

Keywords:

• body condition
• colostrum
• growth
• live weight
• rib fat
• summit metabolic rate

Introduction

Lamb survival and growth to weaning are vital to the profitability of sheep production systems (Young et al. 2011, 2014). Lamb growth to weaning and survival is influenced by a number of factors including ewe nutrition during both pregnancy (Greenwood et al. 2010; Behrendt et al. 2011) and lactation (Coop et al. 1972), ewe body condition score (BCS) (Kenyon et al. 2014) and genetics (Borg et al. 2009). Inadequate ewe nutrition during late pregnancy can adversely affect lamb fetal growth, organ development and energy reserves (Greenwood et al. 2010), thereby placing the lamb at risk of death due to starvation and exposure (Dalton et al. 1980; Alexander 1984; Nowak & Poindron 2006). In addition, sub-optimal nutrition during late pregnancy has consequences for the ewe resulting in reduced energy reserves (Gibb & Treacher 1980; Vernon et al. 1985) and retarded mammary gland development (Mellor et al. 1987; Tygesen et al. 2008). Together these consequences can result in delayed onset of lactogenesis, reduced colostrum production and a reduction in daily milk yield (Tygesen et al. 2008), causing a reduction in lamb growth and a lower live weight at weaning (Khalaf et al. 1979; O'Doherty et al. 1997; Thompson et al. 2011).

Nutrition of the ewe during lactation influences lamb growth to weaning and weaning live weight (Gibb & Treacher 1982; Thompson et al. 2011). In the ewe, sub-optimal nutrition during this period can result in a decrease in the daily milk yield of the ewe and a reduced period of maximal milk production (Langlands 1977; Jordan & Mayer 1989). As lamb growth to weaning is largely a result of milk intake, a decrease in the milk yield of the ewe is likely to result in a decrease in lamb growth rate (Langlands 1977; Kenyon & Webby 2007).

Lamb birth weight, growth to weaning and weaning weight can also be affected by ewe BCS in late pregnancy and lactation (Kenyon et al. 2014), although these effects have been inconsistent. Prior to lambing, greater BCS of the ewe has been shown to have either no effect on lamb birth weight (Gibb & Treacher 1980, 1982; Al-Sabbagh et al. 1995) or a positive effect (Hossamo et al. 1986; Molina et al. 1991). Similarly, lamb weaning weights have been reported to be unaffected by increased ewe BCS (Hossamo et al. 1986; Al-Sabbagh et al. 1995; Aliyari et al. 2012) or to show a positive effect (Molina et al. 1994; Sejian et al. 2009; Kenyon & Hickson et al. 2012). It is possible that this inconsistency results from differences in ewe nutrition in late pregnancy and lactation.

The present study examined the potential interaction between ewe BCS and feeding treatment in very late pregnancy, and lactation, on twin-bearing ewe and lamb performance to weaning. It was hypothesised that twin-bearing ewe and lamb performance would be enhanced with greater ewe BCS when ewes were exposed to low feeding levels. In contrast, no such benefit would occur when ewes were fed at higher levels.

Materials and methods

Experimental design and animals

The 17-day breeding period began on 15 April 2012. In the period from breeding until pregnancy diagnosis, ewes were grazed under commercial farming conditions as part of a larger commercial flock (n = 1207) with pasture masses that did not drop below 1000 kg DM/ha.

At pregnancy diagnosis 93 days after the start of the breeding period (P93), 297 twin-bearing Romney ewes aged between 3 and 5 years and weighing on average 68.7 kg were selected from a commercial flock based on BCS. The selected ewes had a BCS of 2.0 (n = 97), 2.5 (n = 100) or 3.0 (n = 100) (Jefferies 1961; Kenyon et al. 2014). At P96, selected ewes were transferred to the research farm and were given an anthelmintic (Bionic Capsule, Merial/Ancare NZ Ltd, which releases albendazole and abamectin over 100 days). The day after arrival ewes were rescanned to confirm their pregnancy status.

From P98 until P141, all ewes were managed as a single mob with target pre- and post-grazing pasture masses of 1200 and 800 kg DM/ha, respectively. These grazing conditions have previously been reported to allow total ewe live weight to increase with expected conceptus mass (Rattray et al. 1981; Morris & Kenyon 2004; Kenyon & Webby 2007).

At P141, 294 ewes were randomly allocated to either a ‘Low’, ‘Intermediate’ or ‘High’ ryegrass-white clover feeding treatment until the weaning of their lambs 79 days after the mid-point of lambing (L79). Due to ill health, three ewes were not allocated to feeding treatments. A stratified random allocation was used to ensure that each feeding treatment included approximately equal numbers of ewes from each BCS group as recorded at P93 (2.0BCS: Low n = 32, Intermediate n = 32, High n = 30; 2.5BCS: Low n = 33, Intermediate n = 33, High n = 34; 3.0BCS: Low n = 33, Intermediate n = 34, High n = 33).

The Low feeding treatment aimed to ensure pasture masses were maintained within the range of 800–1000 kg DM/ha, the Intermediate treatment within a range of 1200–1400 kg, and the High treatment within a range of 1500–1700 kg DM/ha. It has previously been reported that the intake of multiple ewes is not restricted under ryegrass-white clover masses above 1200 kg DM/ha (Morris et al. 1994; Morris & Kenyon 2004). The total area utilised in this study was 30 ha.

The study was conducted at Massey University's Keeble Farm, 5 km south of Palmerston North, New Zealand (40°S, 175°E) during the period July to December 2012 with approval from the Massey University Animal Ethics committee.

Animal measurements

Ewe BCS (scale 1.0–5.0 including half units; Jefferies 1961; Kenyon et al. 2014) was recorded at P93 (ewe selection), P140, L18 and L79 by a single experienced technician. Live weights of ewes were recorded within 1 hour of removal from pasture (unfasted) at P98, P140, L18 and L79. On the day after the weights were recorded on P98 and P140 and on L79, rib fat depth of the ewes was measured (over the 12th rib, 50 mm from the mid-line) using ultrasound.

During twice-daily lambing inspections (at approximately 0800 h and 1600 h) new lambs, if more than 3 hours old, were tagged, identified to their dam and had their sex, birth weight and birth rank recorded regardless of whether alive or dead at the time of tagging. In addition, the crown to rump length (the distance from the crown of the head to the base of the tail) and thoracic girth (the circumference of the chest immediately posterior to the forelimbs) were recorded. Live weights of the lambs were also recorded at L18 and L79. The presence of a lamb at L79 was used as a proxy measure for survival to weaning.

Blood samples for analysis of indices of colostrum intake (glucose and gamma glutamyltransferase [GGT]) were collected by jugular venepuncture (serum, Becton Dickinson Vacutainer Systems, USA) from a random cohort of 156 live sets of twin lambs at 24–36 hours of age (312 individuals; 2.0BCS: Low n = 32, Intermediate n = 26, High n = 32; 2.5BCS: Low n = 42, Intermediate n = 36, High n = 40; 3.0BCS: Low n = 34, Intermediate n = 38, High n = 32). Immediately after collection, blood samples were placed on ice until centrifugation at 1000 g for 15 min. The serum samples were then frozen at –20 °C until analysed for glucose (Roche Diagnostics, Basel, Switzerland) and GGT activity (Roche Diagnostics, Basel, Switzerland).

In addition, at 24–36 hours of age, 77 live sets of twin lambs (154 individuals; 2.0BCS: Low n = 18; Intermediate n = 16, High n = 20; 2.5BCS: Low n = 18, Intermediate n = 18, High n = 14; 3.0BCS: Low n = 16, Intermediate n = 16, High n = 18) were subjected to indirect open-circuit calorimetry using one of two identical testing chambers (McCutcheon et al. 1983; Kerslake et al. 2010). Briefly, the oxygen consumption of the lamb was measured using a sealed hood which was placed over the head of the lamb. The body temperature of the lamb was recorded using a rectal temperature probe. The lamb was acclimatised to temperatures of 6–8 °C for a total of 12 min. During this time, rectal temperature and oxygen consumption measurements were taken over three successive 4 min periods to obtain a stabilised metabolic rate to allow the base heat production to be calculated. At the end of 12 min, lambs were exposed to conditions to induce summit metabolic rate (maximal heat production). Artificially chilled water (1 °C) was applied through sprinklers at a standardised rate of 1.08 L/min. In addition, cold air was passed over the lamb at a speed of 1.0 m/s. After 20 min, the speed of the cold air was increased to 1.5 m/s, and after another 20 min to 2.0 m/s. The rate of cold air then stayed constant for the remaining period of time. Rectal temperature and oxygen consumption measurements were taken at 4 min intervals for a maximum of 88 min, or until the lamb reached its summit metabolic rate. Summit metabolic rate was determined to have been met when the rectal temperature of the lamb declined at the rate of 1 °C/20 min and there was no further increase in the consumption rate of oxygen (Alexander 1962). To facilitate heat loss, and to encourage heat production to reach a maximum, all lambs with a birth weight above 4 kg had the wool clipped from their back and sides leaving a wool depth of 3 mm. The summit metabolic rate was calculated from oxygen consumption using the following formula (Revell et al. 2002):

After the completion of the monitoring period, lambs were dried and placed in a heated room for 1 h. All lambs were fitted with a woollen coat when returned to their dams.

At L79, a random cohort of 89 complete sets of live twin lambs had their rib fat depth measured (178 individuals; 2.0BCS: Low n = 20, Intermediate n = 20, High n = 20; 2.5BCS: Low n = 20, Intermediate n = 20, High n = 20; 3.0BCS: Low n = 18, Intermediate n = 20, High n = 20). The rib fat depth of lambs was measured over the 12th rib, 50 mm from the mid-line using ultrasound.

Pasture mass and quality measures

During pregnancy (P98–P141) the ewes were moved as required to ensure that the desired pre- and post-grazing targets were met. Each time ewes were moved, pre- and post-grazing masses were recorded using a rising plate meter (Ashgrove Pastoral Products, New Zealand, 50 readings per paddock) with a standard calibration (Pasture mass = [158 × average meter reading] + 200; Hodgson et al. 1999). Once weekly, both pre- and post-grazing sward surface heights of all paddocks were measured using a sward stick (Jenquip, New Zealand, 50 readings per paddock). During the period P142 to L79, grazing pasture masses were recorded approximately weekly and sward surface heights approximately fortnightly.

At P120 and P134, pre-grazing pasture grab samples, which replicated the sward the ewes were consuming, were collected. The samples were frozen at –20 °C until analysis using near infrared reflectance (NIR) to determine the metabolisable energy (ME) content of the pasture. A Bruker MPA NIR spectrophotometer was used to scan the samples and the resulting NIR spectra were analysed using Optic user software (OPUS) version 5.0 (Ettlingen, Germany). Additional pastures samples were collected in lactation (L22, L29, L38, L45, L67, L75) from all three feeding treatments.

Statistical analysis

Complete ewe and lamb data were collected from 270 of the original 291 twin-bearing ewes (2.0BCS: Low n = 28, Intermediate n = 29, High n = 29; 2.5BCS: Low n = 30, Intermediate n = 30, High n = 33; 3.0BCS: Low n = 32, Intermediate n = 28, High n = 31). The non-inclusion of data from 27 ewes was due to eight ewes having one or more dead lambs at tagging (2.0BCS: Low n = 1, Intermediate n = 1, High n = 1; 2.5BCS: Low n = 2, High n = 1; 3.0BCS: Low n = 1, Intermediate n = 1). In addition, seven ewes were removed due to either ill-health or death (three died prior to feeding treatment allocation (all in the 2.0BCS group) and four died during the lambing period (3.0BCS: Intermediate n = 2; 3.0BCS: High n = 2). Twelve ewes were excluded with incomplete lambing data (2.0BCS: Low n = 3, Intermediate n = 2; 2.5BCS: Low n = 1, Intermediate n = 3; 3.0BCS: Intermediate n = 3).

Pasture masses during pregnancy, both pre- and post-grazing, average grazing masses during lactation, and sward surface heights throughout the study were analysed using a generalised linear model in SAS (SAS Institute Inc, Cary, NC, USA). The models contained the fixed effect of feeding treatment.

The study was designed to determine the potential interaction of ewe BCS and ewe feeding treatment from very late pregnancy through to weaning on ewe and lamb parameters. Therefore, in all models of the ewe and lamb dependent variables, the interaction of ewe BCS group and feeding treatment was included in the model regardless of whether or not the interaction was significant (P < 0.05).

Ewe live weight, BCS, change in BCS from pregnancy scanning until weaning, and rib fat depth were analysed using a generalised linear model. The models of data collected during pregnancy contained the fixed effects of ewe BCS group (2.0BCS, 2.5BCS and 3.0BCS) and feeding treatment (Low, Intermediate and High) and their interaction. The models of data collected during lactation also contained the fixed effect of rearing rank at weaning (Twin that reared a Singleton [Twin-Singleton] or Twin that reared a Twin [Twin-Twin]). The models of lactation data also contained lambing date as a covariate.

Lamb live weight and rib fat depth were analysed using a generalised linear model. The model of live weight at birth contained the fixed effects of ewe BCS group and feeding treatment and their interaction. The model also contained the fixed effect of sex of the lamb, the covariate of date of birth and the random effect of ewe. The models of lamb live weight at L18 and L79 contained the fixed effects of the sex of the lambs, rearing rank at weaning, and the two-way interaction of ewe BCS and feeding treatment. Interactions with rearing rank that were not significant (P > 0.05) were removed from the model, which was then rerun.

Lamb serum concentrations of glucose and GGT were not normally distributed and could be normalised using mathematical transformations. Both variables were analysed using the non-parametric Wilcoxon rank sums test. The test is limited to the analysis of single fixed effects, therefore, ewe BCS and feeding treatment were tested separately.

Lamb summit metabolic rate was analysed using a generalised linear model that contained the fixed effects of ewe BCS group and feeding treatment and their two-way interaction. The model also contained the fixed effect of sex of the lamb and the covariates of date of birth and body surface area of the lambs (calculated using the crown rump length and thoracic girth using the formula given by Kerslake et al. (2009) Surface area = 2π(girth)(CRL) + 2π(girth)) and the random effect of testing chamber (Chamber 1 or 2).

Lamb survival was analysed using a generalised model with a binomial distribution and logit transformation. The model included the fixed effects of ewe BCS group and feeding treatment, their two-way interaction and the sex of the lamb.

Results

Pasture mass, sward surface height and pasture quality

Pre- and post-grazing pasture masses between P98 and P140 were 1154 ± 19 and 823 ± 20 kg DM/ha, respectively. At the commencement of feeding treatments (P140), the pasture mass of the Low treatment was lower (P < 0.05) than the Intermediate treatment, which was in turn lower (P < 0.05) than the High treatment (889 ± 41, 1293 ± 41 and 1538 ± 41 kg DM/ha, respectively). These differences (P < 0.05) were maintained throughout lactation (P140–L79) with average pasture masses for the Low, Intermediate and High treatments of 902 ± 33, 1226 ± 33 and 1718 ± 34 kg DM/ha, respectively.

In the period between P98 and P140, the pre- and post-grazing sward surface heights were 3.6 ± 0.41 and 2.0 ± 0.34 cm, respectively. At the commencement of feeding treatments (P140), the sward surface heights of the Low treatment were lower (P < 0.05) than the Intermediate treatment, which were in turn lower (P < 0.05) than the High treatment (2.0 ± 0.40, 4.1 ± 0.40 and 6.0 ± 0.40 cm, respectively). These differences (P < 0.05) were maintained throughout lactation (P140–L79) with average sward surface heights for the Low, Intermediate and High treatments of 2.0 ± 0.30, 3.4 ± 0.30 and 6.8 ± 0.30 cm, respectively.

The ME of the pasture offered to ewes prior to the start of the feeding treatments was 12.9 MJ/kg DM and between P140 and L79 did not differ between the Low, Intermediate and High treatments (P > 0.05; 12.5 ± 0.18, 12.8 ± 0.18 and 12.8 ± 0.18 MJ/kg DM, respectively).

Ewe live weight

On P98, the live weights of the ewes in the 2.0BCS, 2.5BCS and 3.0BCS groups were 64.2 ± 0.55, 68.5 ± 0.55 and 73.2 ± 0.55 kg, respectively (P < 0.05). At the commencement of the feeding treatments (P140), the live weight differences among ewes in the three BCS groups were still present (P < 0.05), however, the live weights of ewes allocated to each of the feeding treatments did not differ (P > 0.05; Table 1).

Table 1 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) and their interaction on mean (± SEM) ewe live weight at P140, L18 and L79.

Ewe live weight (kg)
	n	P140	n	L18	n	L79
Rearing rank
Twin-Singleton			27	78.8^b ± 1.35	31	82.8^b ± 1.28
Twin-Twin			230	73.8^a ± 0.46	226	76.6^a ± 0.48
Body condition score group
2.0BCS	86	76.2^a ± 0.66	83	73.4^a ± 0.96	83	77.7^a ± 0.97
2.5BCS	93	79.8^b ± 0.64	90	76.1^b ± 0.97	90	79.2^a ± 0.92
3.0BCS	91	83.7^c ± 0.65	84	79.5^c ± 0.91	84	82.2^b ± 0.91
Feeding treatment
Low	90	80.0 ± 0.65	85	75.3 ± 0.93	85	74.9^a ± 0.93
Intermediate	87	79.7 ± 0.66	83	76.4 ± 0.96	83	78.8^b ± 0.94
High	93	79.9 ± 0.64	89	77.3 ± 0.95	89	85.3^c ± 0.92
Body condition score group × Feeding treatment^1
2.0BCS × Low	28	75.1^a ± 1.16	27	70.2^a ± 1.43	27	70.2^a ± 1.46
2.0BCS × Intermediate	29	77.5^ab ± 1.14	28	75.6^bc ± 1.47	28	78.7^bc ± 1.50
2.0BCS × High	29	75.9^a ± 1.14	28	74.5^bc ± 1.43	28	84.1^de ± 1.46
2.5BCS × Low	30	80.4^bcd ± 1.12	28	76.1^bcd ± 1.47	28	76.0^b ± 1.45
2.5BCS × Intermediate	30	78.2^abc ± 1.12	29	74.3^b ± 1.43	29	76.4^b ± 1.42
2.5BCS × High	33	80.7^cd ± 1.07	33	77.8^cd ± 1.38	33	85.2^e ± 1.33
3.0BCS × Low	32	84.3^e ± 1.08	30	79.6^d ± 1.36	30	78.6^bc ± 1.40
3.0BCS × Intermediate	28	83.4^de ± 1.16	26	79.4^d ± 1.44	26	81.5^cd ± 1.45
3.0BCS × High	31	83.2^de ± 1.13	28	79.5^d ± 1.46	28	86.6^e ± 1.46

^a,b,c,d,eMeans within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

At L18, there was a significant two-way interaction between BCS group and feeding treatment (Table 1, P < 0.05). Ewe live weights within the 3.0BCS group did not differ among the feeding treatments (P > 0.05). The 2.0BCS group ewes, however, were lighter in the Low feeding treatment than in either the Intermediate or High feeding treatments (P < 0.05; Table 1). In addition, within the 2.5BCS group those ewes that were offered the Intermediate feeding were lighter than ewes offered the High feeding treatment but did not differ from those offered the Low treatment (P < 0.05; Table 1).

At L79, there was a two-way interaction between the BCS group and feeding treatment (P < 0.05; Table 1). Within the 2.0BCS group, ewes offered Low feeding were lighter (P < 0.05) than ewes offered Intermediate feeding which, in turn, were lighter than ewes offered High feeding. However, the live weights of ewes in the 2.5BCS and 3.0BCS groups did not differ between ewes that were offered either the Low or Intermediate feeding treatment (P > 0.05); but for both of those BCS groups, ewes offered the Low and Intermediate feeding treatments were lighter than those offered High feeding (P < 0.05; Table 1).

At both L18 and L79, ewes that reared twin lambs were lighter than ewes that reared a singleton lamb (P < 0.05; Table 1).

Ewe body condition score and rib fat depth

At P140, the BCS of ewes differed between each of the three BCS groups (P < 0.05). Ewes were managed as a single mob until P140, therefore, there were no differences in ewe live weight at P140 between feeding treatments nor was there an interaction of BCS and feeding treatment (P > 0.05; Table 2).

Table 2 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) on mean (± SEM) ewe body condition scores at P140, L18 and L79 and the change in ewe live weight between pregnancy diagnosis and weaning (∆ to weaning).

Ewe body condition score
	n	P140	n	L18	n	L79	n	∆ to weaning
Rearing rank
Twin-Singleton			27	2.67^b ± 0.07	31	2.79^b ± 0.07	31	0.3^b ± 0.10
Twin-Twin			23	2.44^a ± 0.02	226	2.49^a ± 0.03	226	0.0^a ± 0.03
Body condition score group
2.0BCS	86	1.99^a ± 0.02	83	2.16^a ± 0.05	83	2.35^a ± 0.05	83	0.3^c ± 0.11
2.5BCS	93	2.50^b ± 0.02	90	2.57^b ± 0.05	90	2.59^b ± 0.05	90	0.1^b ± 0.08
3.0BCS	91	2.94^c ± 0.02	84	2.94^c ± 0.05	84	2.99^c ± 0.05	84	0.0^a ± 0.07
Feeding treatment
Low	90	2.47 ± 0.02	85	2.46^a ± 0.05	85	2.34^a ± 0.05	85	−0.1^a ± 0.08
Intermediate	87	2.48 ± 0.02	83	2.62^b ± 0.05	83	2.65^b ± 0.05	83	0.1^b ± 0.10
High	93	2.48 ± 0.02	89	2.58^b ± 0.05	89	2.93^c ± 0.05	89	0.4^c ± 0.08
Body condition group × Feeding treatment^1
2.0BCS × Low	28	1.98^a ± 0.04	27	2.02^a ± 0.07	27	1.99^a ± 0.08	27	−0.1^ab ± 0.13
2.0BCS × Intermediate	29	2.01^a ± 0.04	28	2.27^b ± 0.07	28	2.42^bc ± 0.08	28	0.4^bc ± 0.24
2.0BCS × High	29	1.98^a ± 0.04	28	2.18^ab ± 0.07	28	2.63^d ± 0.08	28	0.6^c ± 0.17
2.5BCS × Low	30	2.50^b ± 0.04	28	2.53^c ± 0.07	28	2.34^b ± 0.08	28	0.0^ab ± 0.17
2.5BCS × Intermediate	30	2.51^b ± 0.04	29	2.56^c ± 0.07	29	2.55^cd ± 0.08	29	0.0^ab ± 0.14
2.5BCS × High	33	2.48^b ± 0.04	33	2.62^c ± 0.07	33	2.87^ef ± 0.07	33	0.2^bc ± 0.11
3.0BCS × Low	32	2.92^c ± 0.04	30	2.83^d ± 0.07	30	2.69^de ± 0.08	30	−0.3^a ± 0.11
3.0BCS × Intermediate	28	2.91^c ± 0.04	26	3.03^e ± 0.07	26	2.98^f ± 0.08	26	0.0^ab ± 0.12
3.0BCS × High	31	2.99^c ± 0.04	28	2.95^de ± 0.07	28	3.29^g ± 0.08	28	0.3^bc ± 0.13

^{a,b,c,d,e,f,g}Means within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

At L18, the BCS of ewes in the 2.0, 2.5 and 3.0BCS groups differed from each other (P < 0.05). In addition, within the ewe feeding treatments, ewes offered the Low feeding treatment had lower BCS than ewes offered either Intermediate or High feeding (P < 0.05; Table 2).

At L79, the BCS of ewes differed among the BCS groups, such that 2.0BCS ewes had lower BCS than ewes in the 2.5BCS group, which in turn had lower BCS than the 3.0BCS ewes (P < 0.05). In addition, ewe BCS differed among the feeding treatments, whereby ewes in the Low treatment had lower BCS than ewes in the Intermediate feeding treatment, which in turn had lower BCS than ewes in the High treatment (P < 0.05). There was no interaction of ewe BCS with feeding treatment.

The change in the BCS of ewes between pregnancy scanning and weaning was influenced by weaning rank, feeding treatment, and the BCS of the ewes at the start of the study (pregnancy scanning; P < 0.05); however, there were no two- or three-way interactions (P > 0.05; Table 2). The relationship of BCS group and the change in BCS showed that ewes in the 2.0BCS group gained more condition than those in the 2.5BCS group, which in turn gained more condition than the 3.0BCS group (P < 0.05). There was a positive relationship within the feeding treatments whereby ewes offered greater allowances had greater BCS gains to weaning (P < 0.05). Ewes that reared a single lamb gained more condition between pregnancy scanning and weaning than ewes that reared twins.

At P140, rib fat depth of the ewes reflected the differences in BCS whereby fat depths differed among BCS groups (P < 0.05) but not feeding treatments, nor was there a two-way interaction of BCS and feeding treatment (P > 0.05; Table 3).

Table 3 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) on mean (± SEM) ewe rib fat depth at P140 and L79.

Ewe rib fat depth (mm)
	n	P140	n	L79
Rearing rank
Twin-Singleton			27	7.18^b ± 0.38
Twin-Twin			230	5.13^a ± 0.14
Body condition score group
2.0BCS	86	4.66^a ± 0.17	83	5.33^a ± 0.40
2.5BCS	93	5.88^b ± 0.16	90	5.08^a ± 0.34
3.0BCS	91	8.27^c ± 0.17	84	8.06^b ± 0.30
Feeding treatment
Low	90	6.18 ± 0.17	85	5.06^a ± 0.27
Intermediate	87	6.38 ± 0.17	83	5.86^b ± 0.28
High	93	6.25 ± 0.16	89	7.54^c ± 0.27
Body condition score group × Feeding treatment^1
2.0BCS × Low	28	4.36^a ± 0.30	27	3.94^a ± 0.48
2.0BCS × Intermediate	29	4.98^a ± 0.29	28	5.51^bc ± 0.54
2.0BCS × High	29	4.63^a ± 0.29	28	6.53^cd ± 0.51
2.5BCS × Low	30	6.03^b ± 0.29	28	4.41^ab ± 0.48
2.5BCS × Intermediate	30	5.84^b ± 0.29	29	4.40^ab ± 0.46
2.5BCS × High	33	5.78^b ± 0.27	33	6.42^c ± 0.42
3.0BCS × Low	32	8.14^c ± 0.28	30	6.83^cd ± 0.42
3.0BCS × Intermediate	28	8.32^c ± 0.30	26	7.69^d ± 0.43
3.0BCS × High	31	8.35^c ± 0.29	28	9.66^e ± 0.44

^a,b,c,d,eMeans within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

At L79, however, there was a two-way interaction between BCS group and feeding treatment. Ewes in the 2.5BCS and 3.0BCS groups that were offered either Low or Intermediate feeding treatment had lower fat depths (P < 0.05) than ewes offered the High feeding treatment. Within the 2.0BCS group, ewes offered the Intermediate and High feeding treatment had greater fat depths than ewes offered the Low feeding treatment (P < 0.05; Table 3).

Lamb live weight

There was no interaction of ewe BCS group and feeding treatment for any lamb live weight measures (P > 0.05; Table 4).

Table 4 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) on mean (± SEM) lamb live weight at birth, L18 and L79.

	Lamb live weight (kg)
	n	Birth	n	L18	n	L79
Rearing rank
Twin-Singleton			27	11.5^b ± 0.40	31	31.5^b ± 0.65
Twin-Twin			460	10.5^a ± 0.10	452	28.8^a ± 0.17
Body condition score group
2.0BCS	172	5.1^a ± 0.06	158	10.7^a ± 0.25	159	29.2^a ± 0.42
2.5BCS	186	5.3^b ± 0.06	174	11.1^b ± 0.25	170	30.6^b ± 0.41
3.0BCS	182	5.2^ab ± 0.06	155	11.3^b ± 0.24	154	30.5^b ± 0.40
Feeding treatment
Low	180	5.3 ± 0.06	170	11.2 ± 0.24	159	28.9^a ± 0.41
Intermediate	174	5.2 ± 0.06	159	11.0 ± 0.25	157	29.8^b ± 0.41
High	186	5.2 ± 0.06	158	10.9 ± 0.24	167	31.7^c ± 0.40
Body condition score group × Feeding treatment^1
2.0BCS × Low	56	5.1^a ± 0.10	50	10.9^ab ± 0.34	50	28.0^a ± 0.58
2.0BCS × Intermediate	58	5.1^a ± 0.10	55	10.6^ab ± 0.34	55	28.8^ab ± 0.58
2.0BCS × High	58	5.2^a ± 0.10	53	10.4^a ± 0.33	54	30.8^de ± 0.58
2.5BCS × Low	60	5.3^ab ± 0.10	54	11.2^b ± 0.34	54	29.3^abc ± 0.58
2.5BCS × Intermediate	60	5.2^ab ± 0.10	56	11.1^ab ± 0.33	55	30.4^cd ± 0.57
2.5BCS × High	66	5.5^b ± 0.10	64	11.0^ab ± 0.32	61	32.2^f ± 0.54
3.0BCS × Low	64	5.3^ab ± 0.10	55	11.3^b ± 0.32	55	29.3^bc ± 0.56
3.0BCS × Intermediate	56	5.1^a ± 0.10	47	11.1^ab ± 0.34	47	30.2^bcd ± 0.59
3.0BCS × High	62	5.3^ab ± 0.10	53	11.4^b ± 0.34	52	32.1^ef ± 0.58

^a,b,c,d,e,fMeans within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

The birth weight of lambs born to ewes in the 2.0BCS group was lower than for lambs born to ewes in the 2.5BCS group (P < 0.05; Table 4), but lambs born to ewes in the 3.0BCS group were intermediate and did not differ from the other two BCS groups. There was no effect of ewe feeding treatment on lamb birth weight (P > 0.05).

At L18, lambs born to ewes in both the 2.5BCS and 3.0BCS groups were heavier than lambs born to ewes in the 2.0BCS group (P < 0.05, Table 4). As with lamb live weight at birth, ewe feeding treatment had no effect on lamb live weight at L18 (P > 0.05). Lambs that were reared as a twin were lighter than lambs reared as a singleton (P < 0.05).

At L79, the live weight of lambs born to ewes in the 2.5BCS and 3.0BCS groups was greater than that of lambs born to ewes in the 2.0BCS group (P < 0.05, Table 4). Lambs born to ewes in the Low feeding treatment were lighter than lambs born to ewes in the Intermediate treatment, which in turn were lighter than lambs born to ewes in the High treatment (P < 0.05). Lambs reared as a twin were lighter than lambs reared as a singleton (P < 0.05).

Indices of colostrum uptake

There was no effect of ewe BCS group or feeding treatment (P > 0.05) on lamb serum glucose or GGT concentrations at approximately 24 hours of age (Table 5).

Table 5 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) on back-transformed logit mean (and 95% confidence interval) lamb serum glucose (mmol/L) and GGT (iu) concentrations and summit metabolic rate mean (± SEM) at 24 hours of age.

Serum concentrations
	n	Glucose (mmol/L)	n	GGT (iu)	n	Summit metabolic rate (W/kg)
Body condition score group
2.0BCS	90	6.4 (6.38–7.12)	90	1952 (1974–2551)	54	20.9^b ± 0.38
2.5BCS	118	6.5 (6.36–6.93)	118	1809 (1852–2347)	50	20.4^b ± 0.40
3.0BCS	104	6.7 (6.30–7.23)	104	1739 (1857–2505)	50	19.3^a ± 0.40
Feeding treatment
Low	108	6.4 (6.24–6.62)	108	2008 (2015–2655)	52	20.3 ± 0.39
Intermediate	100	6.6 (6.27–7.35)	100	1819 (1779–2287)	46	20.3 ± 0.39
High	104	6.7 (6.59–7.25)	104	1791 (1869–2415)	52	20.0 ± 0.39
Body condition score group × Feeding treatment^1
2.0BCS × Low	32	6.2 (5.84–6.59)	32	2301 (1897–2728)	18	21.2^b ± 0.63
2.0BCS × Intermediate	26	7.1 (6.63–8.60)	26	1837 (1549–2634)	16	21.0^b ± 0.67
2.0BCS × High	32	6.3 (6.07–7.08)	32	1702 (1768–2938)	20	20.5^ab ± 0.70
2.5BCS × Low	42	6.4 (6.10–6.56)	42	1976 (1708–2588)	18	20.9^b ± 0.75
2.5BCS × Intermediate	36	6.4 (5.91–7.20)	36	1657 (1592–2418)	18	20.2^ab ± 0.66
2.5BCS × High	40	7.0 (6.48–7.63)	40	1861 (1671–2595)	14	20.1^ab ± 0.66
3.0BCS × Low	34	6.7 (6.35–7.17)	34	1732 (1785–3390)	16	18.8^a ± 0.66
3.0BCS × Intermediate	38	6.6 (5.37–7.62)	38	1919 (1583–2455)	16	19.6^ab ± 0.70
3.0BCS × High	32	6.8 (6.43–7.74)	32	1610 (1544–2338)	18	19.5^ab ± 0.70

^a,bMeans within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

Lamb summit metabolic rate

The summit metabolic rate of lambs born to ewes in the 3.0BCS group was lower than lambs born to both 2.0 and 2.5BCS groups (P < 0.05; Table 5). There was, however, no effect of ewe feeding treatment or two-way interaction of ewe BCS and feeding treatment on lamb summit metabolic rate (P > 0.05).

Lamb rib fat depth at L79

Rib fat depths of lambs born to ewes in the Low and Intermediate feeding treatments were lower than lambs born to ewes in the High feeding treatment (P < 0.05, Table 6). Lambs born to ewes in the 3.0BCS group tended to have greater fat depths than lambs born to ewes in the 2.5BCS group (P = 0.07). There was no interaction of ewe BCS and feeding treatments on rib fat depth (P > 0.05).

Table 6 Effect of ewe body condition score group (2.0BCS vs 2.5BCS vs 3.0BCS) and feeding treatment in very late pregnancy and lactation (Low vs Intermediate vs High) on mean (± SEM) lamb rib fat depth at L79 and back-transformed logit mean (95% confidence interval) lamb survival to L79.

Lamb measures
	Rib fat depth (mm)		Survival (%)		Litter weight (kg)
	n	L79	n	L79	n	L79
Body condition score group
2.0BCS	60	2.5 ± 0.11	159	93.5^b (88.6–96.4)	86	51.6 ± 1.7
2.5BCS	58	2.5 ± 0.11	170	91.7^b (86.8–94.9)	93	53.6 ± 1.6
3.0BCS	60	2.8 ± 0.10	154	84.8^a (78.8–89.4)	91	49.8 ± 1.7
Feeding treatment
Low	58	2.4^a ± 0.11	159	91.7 (86.5–95.1)	90	48.7^a ± 1.7
Intermediate	60	2.4^a ± 0.10	157	88.7 (83.1–92.6)	87	51.2^ab ± 1.7
High	60	2.9^b ± 0.10	167	91.1 (85.5–94.7)	93	55.0^b ± 1.6
Body condition score group × Feeding treatment^1
2.0BCS × Low	20	2.3^a ± 0.18	50	89.1 (77.7–95.0)	28	47.3^a ± 3.0
2.0BCS × Intermediate	20	2.5^ab ± 0.18	55	95.1 (85.7–98.4)	29	52.3^ab ± 3.0
2.0BCS × High	20	2.8^bc ± 0.18	54	95.0 (85.4–98.4)	29	55.1^ab ± 3.0
2.5BCS × Low	18	2.3^a ± 0.19	54	90.5 (80.3–95.7)	30	50.3^ab ± 2.9
2.5BCS × Intermediate	20	2.3^a ± 0.18	55	91.8 (81.8–96.6)	30	53.1^ab ± 2.9
2.5BCS × High	20	2.9^bc ± 0.18	61	92.6 (83.4–96.9)	33	57.5^b ± 2.8
3.0BCS × Low	20	2.7^abc ± 0.18	55	86.1 (75.2–92.6)	32	48.6^a ± 2.8
3.0BCS × Intermediate	20	2.5^ab ± 0.18	47	83.2 (70.7–91.0)	28	48.3^a ± 3.0
3.0BCS × High	20	3.1^c ± 0.18	52	85.1 (74.1–91.9)	31	52.4^ab ± 2.9

^a,b,cMeans within columns and main effects with different letters are significantly different (P < 0.05).

¹Ewe body condition score group by feeding treatment interaction.

Lamb survival

Survival of lambs to weaning was greater for lambs born to ewes in the 2.0BCS and 2.5BCS groups than ewes in the 3.0BCS group (P < 0.05, Table 6). There was no effect of ewe feeding treatment or a two-way interaction between ewe BCS group and feeding treatment on lamb survival (P > 0.05).

Total lamb litter live weight per ewe at L79

The total litter weight of lambs weaned per ewe was greater for ewes in the High feeding treatment than the Low treatment (P < 0.05; Table 6). Ewe BCS tended to affect litter weights such that ewes in the 3.0BCS group tended to have lower litter weights than those in the 2.5BCS group (P = 0.1). The two-way interaction between BCS group and feeding treatment had no effect on lamb litter live weight (P > 0.05).

Discussion

The pasture masses measured during lactation indicate that the target feeding treatments were met, thus allowing for the effects of the feeding treatment to be tested. In addition, at allocation to feeding treatments in late pregnancy, the differences in BCS allowed for the testing of the hypothesis that twin-bearing ewe and lamb performance would be enhanced by greater BCS when feeding levels were low in very late pregnancy and lactation, but that no such benefit would be observed at the higher feeding levels. It is acknowledged that the selection of ewes in differing condition scores may have resulted in the unintentional selection of ewes with underlying health problems or genetic predisposition to leanness (Kenyon et al. 2014). However, the change in BCS observed between pregnancy scanning and weaning demonstrated that ewes in the 2.0BCS group had the capacity to gain condition. In this study, therefore, BCS has been used solely as an indicator of ewe performance.

Given that the feeding treatments were applied in very late pregnancy it may not be surprising that there was no effect of feeding treatment on lamb birth weight, indices of colostrum intake or summit metabolic rate. It has been previously shown that feeding treatments in very late pregnancy have either no impact or a minimal impact on lamb birth weight (Kenyon & Morris et al. 2011; Kenyon & van der Linden et al. 2011), colostrum uptake (Kenyon & van der Linden et al. 2011) or summit metabolic rate (Kerslake et al. 2009). It is also important to acknowledge that in the present study the nutritional management of the ewes prior to the start of the feeding treatments allowed the ewes to gain in total body weight at a level similar to expected conceptus mass (Rattray et al. 1974), allowing the ewes to maintain their BCS. This suggests that ewes were not exposed to conditions that required them to meet the increased energy demands of pregnancy by utilising their own body reserves.

Lambs born to ewes in the High feeding treatment were heavier at weaning than lambs born to ewes in the Intermediate treatment, which in turn, were heavier than lambs born to ewes in the Low treatment. Previously, it had been reported that lamb live weight at weaning (or growth to weaning) increased as pasture heights increased up to 6 cm during the 10 weeks period post-lambing (the equivalent of 1800 kg DM/ha; Kenyon & Webby 2007). Similarly, Thompson et al. (2011) reported that lamb growth rate to weaning plateaued for ‘food-on-offer’ values greater than 2500 kg DM/ha, which is approximately equivalent to sward surface heights of 7 cm (Hyder et al. 2004). In contrast, Morris & Kenyon (2004) reported that lamb live weight at weaning did not differ between pasture masses of approximately 1200 and 2000 kg DM/ha, respectively. In support of the lamb live weight effect, ewe live weight, body condition and rib fat depth at weaning were greatest in the High followed by the Intermediate and then Low feeding treatments. Ewe feeding treatment, however, had no effect on the survival of lambs to weaning but did affect the total weight of lamb weaned per ewe. Ewes in the High group weaned a greater weight of lamb compared with the Low group. Combined, these results indicate that lamb performance is enhanced by the High feeding treatment. The lack of an influence of the Intermediate feeding treatment on the weight of lamb weaned may be an artefact of the lower lamb survival seen in the lambs of that treatment group. The live weights of the individual lambs at weaning indicated that both Intermediate and High feeding increased lamb live weight. If farmers wish to maximise twin-bearing ewe and lamb performance at weaning they need to ensure pasture masses in lactation are at least 1200–1400 kg DM/ha but can be enhanced further with greater masses of 1500–1700 kg DM/ha. Identifying the pasture mass that maximises ewe and lamb performance warrants further investigation.

Lambs born to ewes with a BCS of 2.0 were consistently lighter from birth to weaning than lambs born to ewes with a greater condition. It has previously been reported that ewe BCS is positively related to lamb live weight (Molina et al. 1991; Sejian et al. 2009) or that the live weight of lambs born to ewes with a BCS of 2.0 was lower than those born to ewes with a BCS of 2.5 or 3.0 (Kenyon & Morris et al. 2011; Kenyon & Morris et al. 2012; Kenyon & Hickson et al. 2012). Ewe BCS is also known to positively affect ewe milk production (Gibb & Treacher 1980; Hossamo et al. 1986). The results of the present study indicate that twin-bearing ewes should have a minimum BCS of 2.5 in late pregnancy to maximise lamb weaning weight.

Ewe BCS had no effect on apparent colostrum uptake in the present study. It has been previously reported that ewes with a BCS of 2.5 to 3.5 tend to produce more colostrum than higher or lower conditioned ewes (Al-Sabbagh 2009), however, there is little information available on the intake of colostrum of lambs born to ewes with differing condition.

Lambs born to ewes with a BCS of 3.0 displayed a decrease in both summit metabolic rate and survival to weaning. This result is contrary to previous studies, which have shown a positive effect of the BCS of the ewe on lamb survival (Litherland et al. 1999; Kleemann & Walker 2005; Everett-Hincks & Dodds 2007) or no effect (Al-Sabbagh et al. 1995; Litherland et al. 1999).

To these authors' knowledge, the effect of the BCS of the ewe on the summit metabolic rate of the lamb has not been previously reported. The lower summit metabolic rate may help to explain the lower survival observed in the lambs born to ewes with a BCS of 3.0 compared with lambs born to ewes with a lower condition. Further studies are required to verify this effect and to determine what the mechanism might be that is responsible for this apparent effect.

In all lamb parameters measured, there was no interaction between ewe feeding and BCS. This indicates that the benefit from a greater BCS was consistent across all feeding treatments although in absolute terms the differences were small. This further emphasises the importance of ensuring ewes are of adequate condition in late pregnancy.

Conclusion

Offering ewes a high level of feeding during very late pregnancy and lactation and having ewes with a BCS greater than 2.0 resulted in greater lamb live weights at weaning; however, there was no interaction of ewe feeding with BCS. Therefore, these results indicate that there are benefits to avoiding low ewe condition in late pregnancy and lactation across a wide range of herbage masses. The results of this study indicate that to ensure high performance of twin-bearing ewes that have been offered adequate nutrition in mid and late pregnancy, farmers should ensure ewes have a BCS of 2.5 or 3.0 and are offered pasture masses of more than 1200 kg DM/ha in very late pregnancy and lactation.

Acknowledgements

The authors wish to acknowledge Mr Dean Burnham and Mr Geoff Purchas for their technical assistance. In addition, the authors wish to thank The C Alma Baker Trust for part-funding RA Corner-Thomas, Gravida for part-funding PR Kenyon and Massey University for funding this study.