Effect of nutrition from mid-pregnancy to parturition on the live weight of twin-bearing hoggets and the live weight and survival of their lambs

Abstract

This experiment investigated the effect of two nutritional levels (medium and ad libitum) from day 85 of pregnancy until parturition on the live weight and metabolic status of twin-bearing hoggets, and the gamma-glutamyl transferase and glucose concentration on the day of lambing (L1), survival and live weight of their offspring until L29. The mean live weight of the ad libitum treatment hoggets (66.3±0.6 kg) was greater (P<0.05) at P145 than that of medium treatment hoggets (63.6±0.5 kg). Hogget live weight did not differ (P>0.05) between treatments at L29 (60.9±0.9 vs 60.0±1.0 kg for the medium and ad libitum treatment hoggets, respectively). The birth weight of lambs born to ad libitum ewes (4.0±0.1 kg) was greater (P<0.05) than that of lambs born to medium treatment ewes (3.7±0.1 kg). At L29, lamb live weight did not differ (P>0.05) between treatments (11.2±0.3 vs 11.3±0.3 for the medium and ad libitum treatments, respectively). Lamb survival did not differ (P>0.05) between treatments. There was no difference between treatments in the efficiency of lamb live weight produced. These results indicate that offering twin-bearing hoggets ad libitum levels of herbage from day 85 of pregnancy until parturition is not an efficient technique to increase lamb production from these hoggets. Farmers should, therefore, offer 1000–1400 kg DM/ha to optimize lamb production from twin-bearing hoggets.

Keywords:

• ewe lamb
• adolescent ewe
• nutrition
• lamb survival
• lamb weaning weight

Introduction

Studies involving commercial flocks in New Zealand reported that the proportion of hoggets joined with the ram identified as twin-bearing ranged from 16–32% (Kenyon et al. 2005, 2006; Morris et al. 2005). The increased energy requirement to maintain twin foetuses to term and raise twin lambs to weaning, above the energy requirement for the increasing maternal size of the hogget, requires investigation. Kenyon et al. (2004) reported that the main reason New Zealand farmers were not joining hoggets with the ram was a perceived negative impact of hogget breeding on the subsequent 2-year-old breeding live weight. This perception is supported by Kenyon et al. (2008a). Therefore, management practices for twin-bearing hoggets during pregnancy and lactation require investigation to ensure the target 2-year-old breeding live weight is achieved.

Twin lambs born to mature multiparous ewes offered ad libitum herbage from mid-pregnancy until parturition were heavier at birth (Morris & Kenyon 2004; Corner et al. 2008), but the weaning weights of these lambs were similar (Morris & Kenyon 2004; Everett-Hincks et al. 2005) or heavier (Corner et al. 2008) compared with twin lambs born to mature ewes offered a restricted level of herbage from mid-pregnancy until parturition. In addition, the live weight of the mature multiparous ewes offered ad libitum or a restricted level of herbage from mid-pregnancy until parturition did not differ at weaning (Morris & Kenyon 2004; Corner et al. 2008).

New Zealand pastoral studies (Morris et al. 2005; Kenyon et al. 2008b; Mulvaney et al. 2008) have shown that offering ad libitum compared with medium levels of herbage during pregnancy did not affect the birth weight of single lambs born to hoggets. However, the effect of offering differing herbage levels to twin-bearing hoggets from pregnancy diagnosis until parturition on the lamb birth weight and survival is unknown.

The objective of the present study was to investigate the effect of nutrition from day 85 of pregnancy until parturition on twin-bearing hogget live weight, peripheral metabolite concentrations of hoggets and lambs, the survival and live weight of the lambs until day 29 of lactation.

Materials and methods

Experimental design and animals

A commercial flock of 1786 Composite (½ Romney, ¼ Texel, ¼ Finnish Landrace) hoggets were bred over a 34-day breeding period. At the time of pregnancy diagnosis, via abdominal ultrasound, 450 hoggets were identified as twin-bearing. From these, 180 hoggets were selected to ensure they were between 40 and 50 kg and were used in the study. The average live weight of the hoggets selected at pregnancy diagnosis was 45.9±0.2 kg.

One-hundred-and-two days after ram introduction (average day 85 of pregnancy, range 68–102), the hoggets were randomly allocated to one of two treatment groups (medium or ad libitum) until parturition. The aim of the medium (n=88) treatment was to offer pre-grazing herbage mass of 1400 kg DM/ha , while post-grazing herbage mass did not fall below 900 kg DM/ha. The ad libitum (n=92) treatment group were offered a minimum herbage mass of 1800 kg DM/ha. The hoggets grazed a total area of 20 ha of mixed perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) pasture. The size of the grazing area and grazing interval for both treatment groups was based on herbage mass (i.e. when herbage mass for the medium treatment group fell below 900 kg DM/ha, the hoggets were reallocated herbage, while when the herbage mass for ad libitum treatment group fell below 1800 kg DM/ha, the hoggets were reallocated herbage). All hoggets were set stocked for lambing 154 days after ram introduction (average day 137 of pregnancy, range 120–154 days) at eight hoggets per ha within their nutritional treatments. Each treatment group was allocated to four paddocks with an average herbage mass of 1120±90 kg DM/ha and 1860±70 kg DM/ha for medium and ad libitum treatment, respectively. Approximately 24 h after lambing (L1), all hoggets and their lambs were removed from their respective nutritional treatments and were managed as one group continuously grazed on 1780±65 kg DM/ha from L1 until L29.

The present study was conducted from July until November at Massey University's Keeble farm (latitude 41°10′S, longitude 175°36′E), 5 km south of Palmerston North, New Zealand. The study was approved by the Massey University Animal Ethics Committee.

Hogget measurements

Hoggets were weighed, unfasted (within 1 h off pasture) on P85, P99, P115, P130, P145, 24 h after parturition (L1), 8 days after the midpoint of lambing (L8, range from 5–11 days from lambing), L15, L22 and L29. The hogget live weight gain during the nutritional regime period was calculated from P85 until P145. All pregnant hoggets were weighed weekly during the lambing period until all hoggets had lambed to enable the calculation for conceptus weight.

Plasma collection and analysis

On P137, a 5 mL blood sample was collected from 40 hoggets from each treatment; on L1, a further sample was collected from 20 hoggets and their twin lambs from each treatment (n=120 hoggets and 80 lambs in total). On L1, a sample was collected only if both lambs were present. All blood samples were collected via jugular venepuncture into lithium heparin vacutainers (Becton Dickinson Vacutainer Systems, USA). Immediately after the blood samples were taken, they were placed on ice before centrifuging at 1000 g for 15 min. The plasma was then frozen at −20 °C until analysis. Plasma from hoggets was analysed for glucose and β-hydroxybutyrate (OHB) and the lamb's plasma was analysed for glucose and gamma-glutamyl transferase (GGT). OHB was analysed using enzymatic assays (Osaka, Japan and Illinois, USA), glucose using a hexokinase assay and plasma GGT using the Szasz method (Roche Diagnostics, Germany).

Lamb measurements

Lambs were tagged, identified to their dam and their date of birth, sex and live weight recorded within 12 h of birth (L0). In addition, crown rump length (CRL), thoracic girth circumference (girth), rear leg length (RL, distance from the hip to the tip of the hoof) and foreleg length (FL, distance from the shoulder to the tip of the hoof) were measured. All lambs were reweighed, unfasted at L8, L15, L22 and L29.

Herbage samples

Herbage pluck samples (Wallis de Vries 1995) were collected when the hoggets were moved into a new treatment paddock on P85, P99, P113 and P145. Another sample was collected on L15. The samples from each treatment group were pooled (five samples in total) for analysis of crude protein and metabolizable energy (MJ ME/kg DM). The samples were dried in a convection oven for 12 h at 105 °C. The crude protein and energy content was determined via near-infrared-spectrometry (Bruker MPA NIR spectrophotometer, Ettlingen, Germany). The resulting NIR spectra were analysed using Optic user software (OPUS) version 5.0.

Data analysis

Hogget and lamb live weight, the difference in individual birth weight within the litter, total birth weight (the sum of the individual birth weight within a litter), estimated conceptus weight (weight within 7 days of parturition minus weight 24 h post-lambing), and plasma from the hoggets and the lambs were analysed using the GLM procedure (SAS 2005). In the models for hogget live weight, lamb live weight, the difference in individual birth weight within the litter, total birth weight, estimated conceptus mass, fixed effects of treatment and the sex of the lamb were tested for each parameter. Date of birth was included as a covariate. In the model for hogget plasma, the fixed effect of treatment was included in the model. In the model for lamb plasma, the fixed effect of treatment and the sex of the lamb were tested. In the model for hogget live weight during lactation, fixed effects of rearing rank and treatment during pregnancy and their interactions were tested. Date of birth was included as a covariate. Non-significant (P>0.05) interactions were removed and the model rerun. The proportion of lambs that survived until L29 was analysed using the GENMOD procedure (SAS 2005). The fixed effect of treatment was tested.

Modelling of live weight data

Conceptus-free live weight for each treatment was assumed to be the last live weight prior to parturition for each hogget (within 7 days of parturition) minus the estimated conceptus weight (includes foetal weights, membranes and fluids). The estimated conceptus weight was defined as the last live weight prior to parturition minus the hogget weight 24 h after lambing. The conceptus-free live weight change was assumed to be the conceptus-free live weight minus live weight at the start of the study (45.9±0.2 kg).

The herbage dry matter intake was calculated in two sections. The first section involved estimating the required metabolizable energy (MJ ME) to achieve the conceptus-free live weight change. The average live weight of the hoggets in each treatment was divided into 5 kg sub-categories (45–49, 50–55, 55–59 kg) to align with that provided in Rattray (1986). The MJ ME required was calculated based on the live weight change for each sub-category. The second section provided a total MJ ME required to achieve the total conceptus-free live weight change during the entire period. The total MJ ME ingested was converted into kg DM required to achieve the live weight gain during the 60-day treatment. The energy content of the herbage was assumed to be 12 MJ ME/kg DM.

The efficiency of the system was defined as kilograms of lamb per ewe at L29 per kilogram of estimated dry matter ingested during the treatment period. The total lamb live weight at L29 was estimated using a weighting factor of 1.55 and 1.60 for the medium and ad libitum treatments, respectively. This represented the average number of lambs present at L29 per hogget.

Results

Herbage mass and quality

The mean medium treatment pre- and post-grazing herbage mass was 1350±120 and 950±80 kg DM/ha, respectively and the pre-grazing mass for the ad libitum treatment was 1860±150 kg DM/ha throughout pregnancy.

The pooled crude protein content of the herbage offered was 33.4%, 25.7%, 20.1%, 21.8% and 24.5% and the pooled energy content was 12.0, 12.2, 12.1, 12.5 and 12.0 MJ ME/kg DM on P85, P99, P113, P145 and L15 for both treatments.

Hogget live weight during pregnancy and lactation

Hogget live weight was not affected (P>0.05) by treatment on P85 and P99. However, on P115, P130 and P145, ad libitum treatment hoggets were heavier (P<0.05) than the medium treatment hoggets by 2 to 3 kg (Fig. 1). The live weight change of the ad libitum (343±15 g/day) treatment was higher (P<0.05) than the medium treatment (293±12 g/day). Hogget live weight was heavier (P<0.05) in the ad libitum compared with the medium treatment hoggets on L1, but on L8, L15, L22 and L29. Hogget live weight did not differ (P>0.05) between treatments.

Figure 1.  The effect of nutrition (medium [---] vs ad libitum [—]) from day 85 of pregnancy until parturition on hogget live weight from day 85 of pregnancy (P85) until average lamb age of 29 days (L29) (mean±SE).

The estimated conceptus mass was not affected (P>0.05) by nutrition (9.49±0.49 vs 10.35±0.49 for medium and ad libitum treatments, respectively). The conceptus-free live weight change was 8.2 and 10.0 kg for the medium and ad libitum treatment groups, respectively.

Glucose and OHB concentrations of hoggets

Glucose concentration at P137 and L1 did not (P>0.05) differ between nutritional treatments (Table 1). The OHB concentration did not (P>0.05) differ between treatments at P137. However, OHB concentration at L1 was higher (P<0.05) in the medium treatment hoggets compared with ad libitum treatment hoggets.

Table 1 . The effect of nutrition (medium vs ad libitum) from day 85 of pregnancy until parturition on the mean (±SE) glucose (glucose, mmol/L) and β-hydroxybutyrate (OHB, mmol/L) concentrations of hoggets on day 137 of pregnancy (P137) and 24 h after birth (L1). Within columns, means with different superscripts differ significantly (P<0.05).

		Glucose	OHB
	n
P137
Medium	40	3.31±0.09	0.47±0.03
Ad libitum	40	3.49±0.08	0.47±0.03
L1
Medium	20	4.10±0.21	0.69±0.05^b
Ad libitum	20	4.60±0.20	0.48±0.05^a

Lamb live weight, dimensions and survival

Lambs born to the ad libitum treatment hoggets were heavier (P<0.05) at birth compared with the lambs born to medium treatment hoggets (Table 2). The lamb live weight at L8, L15, L22 and L29 did differ (P>0.05) between treatments. The mean birth weight difference within a litter did not (P>0.05) differ between treatments (0.60±0.1 vs 0.58±0.1 kg for the medium and the ad libitum treatment groups, respectively).

Table 2 . The effect of hogget nutrition (medium vs ad libitum) from day 85 of pregnancy until parturition on the mean live weight (±SE, kg) of twin lambs at birth (L1), 7 days old (L8), L15, L22 and L29. Data within columns with different superscripts differ significantly (P<0.05).

		L1		L8	L15	L22	L29
	n		n
Medium	158	3.73±0.08^a	126	5.61±0.13	7.41±0.17	9.72±0.21	11.18±0.25
Ad libitum	168	4.04±0.08^b	131	5.86±0.13	7.60±0.18	10.07±0.22	11.31±0.26

Crown rump length and rear leg length were longer (P<0.05) in lambs born to the ad libitum treatment hoggets compared with lambs born to the medium treatment hoggets. Thoracic girth circumference and foreleg length did not differ (P>0.05) between nutritional treatments (Table 3).

Table 3 . The effect of treatment (medium vs ad libitum) from day 85 of pregnancy until parturition on the mean (± SE) lamb crown rump length (CRL, cm), thoracic girth (girth, cm), foreleg length (FL, cm) and rear leg length (RL, cm), glucose concentration (mmol/L) and GGT concentration (iU/L). Within columns, means with different superscripts differ significantly (P<0.05).

		CRL	Girth	FL	RL		Glucose	GGT
	n					n
Medium	158	47.87±0.30^a	36.77±0.26	34.98±0.21	35.05±0.19^a	40	6.48±0.26	2163±236
Ad libitum	168	48.75±0.26^b	37.22±0.27	35.34±0.19	35.59±0.19^b	40	6.53±0.27	1752±245

Lamb survival was not affected (P>0.05) by treatment (logit value, −0.12±0.2, back transformed percentage 80% vs −0.18±0.2, 78% for medium and ad libitum treatments, respectively).

Lamb glucose and GGT concentration

On L1, nutrition had no effect (P>0.05) on lamb glucose or GGT concentrations (Table 3).

Modelling of live weight

The estimated conceptus mass was 9.5 and 10.4 kg for the medium and ad libitum treatments, respectively. The estimated conceptus-free live weight at P145 was 54.1 and 55.9 kg for the medium and ad libitum treatments, respectively. Conceptus-free live weight change was 8.2 and 10.0 kg for the medium and ad libitum treatments, respectively. The hoggets carrying lambs until term required 1183 and 1444 MJ ME in the medium and ad libitum treatments, respectively, to achieve their respective conceptus-free live weight change. This equated to 99 and 120 kg DM for the medium and ad libitum treatments, respectively. Therefore, the medium and the ad libitum treatment hoggets produced 0.18 and 0.15 kg of lamb at L29 per kg DM ingested from P85 until P145, respectively.

Discussion

The objective of the present study was to investigate the effect of nutrition commencing on approximately day 85 of pregnancy until parturition on twin-bearing hogget live weight and metabolic indices, lamb live weight, indices of colostrum intake and survival until 29 days of age.

The pre- and post-grazing masses of the medium and ad libitum treatments were met. However, the actual live weight change achieved by both the medium and the ad libitum treatments were much higher (130 and 215 g/day for the medium and ad libitum treatments, respectively) than that previously reported under similar grazing and herbage allowance conditions (Morris et al. 2005; Kenyon et al. 2008b; Mulvaney et al. 2008). The live weight gains resulted in a 3 kg increased live weight for the ad libitum treatment at P145 which was subsequently eliminated after parturition. Rattray et al. (1982) showed that live weight gain plateaus when the post-grazing mass is greater than 1000 kg DM/ha. Therefore, the pre- and post-grazing conditions of 1400 and 1000 kg DM/ha for the medium treatment did not appear to limit intake. The additional herbage allowance offered to the ad libitum treatment did not allow additional maternal live weight. Further experiments with a greater range of nutritional treatment levels may warrant further investigation.

In twin-bearing mature multiparous ewes, increasing the level of pastoral nutrition from mid-pregnancy to parturition increased lamb birth weight under New Zealand pastoral conditions (Morris & Kenyon 2004; Corner et al. 2008). This supports the results obtained in the present study from hoggets. Conversely, pastoral studies involving single-bearing hoggets (Morris et al. 2005; Kenyon et al. 2008b; Mulvaney et al. 2008) and mature multiparous ewes (Kenyon et al. 2009) reported that nutrition did not affect lamb birth weight. This indicates that the birth weight of single- and twin-bearing mature multiparous ewes and hoggets is affected by pastoral nutrition in a similar manner for each age group.

Lamb survival was not affected by maternal nutrition in the present study. Previous pastoral studies (Morris et al. 2005; Kenyon et al. 2008b; Mulvaney et al. 2008, 2010) have shown that the survival of single born lambs was not affected by above maintenance levels of nutrition. Morel et al. (2009) reported lower survival rates in the lighter lamb within a twin litter and that large variation in birth weight was associated with lower survival. The variation in lamb birth weight within litters in the present study did not differ between nutritional groups. The birth weight of the lambs from both treatments was within the optimal range (3.3–4.1 kg) for survival suggested by McMillan & McDonald (1983). The glucose and GGT concentration (an indice of colostrum intake) did not differ between treatments. Therefore, this data would suggest that there would not be a difference between nutritional treatments on lamb survival. In addition, the numbers in the present experiment may not have allowed for a significance to be identified.

Lamb live weight gain until 29 days of age was not affected by nutrition. Previous hogget pastoral studies (Morris et al. 2005; Kenyon et al. 2008b; Mulvaney et al. 2008, 2010) have shown that under similar herbage levels, the live weight of the lamb was not affected by herbage intake. Also, pastoral studies by Morris & Kenyon (2004) and Corner et al. (2008) involving twin lambs born to mature multiparous ewes reported that similar nutritional levels did not affect the lamb weaning live weights. This suggests that nutrition during pregnancy does not affect lamb live weight during lactation of twin lambs born to hoggets.

Hogget live weight did not differ between treatments at L29. However, Morris et al. (2005), Kenyon et al. (2008b) and Mulvaney et al. (2008, 2010) have consistently shown that single-bearing hoggets, offered ad libitum levels of nutrition during pregnancy, were heavier than those offered a medium level during pregnancy. The results of the current experiment indicate that the level of nutrition offered to the medium treatment is not limiting intake. Therefore, it would be expected that the post-grazing mass of 1000 kg DM/ha in the medium treatment was not limiting hogget live weight gain.

The conceptus-free live weight gained during the current experimental period did not differ between the treatments. Each kilogram of dry matter ingested between P85 and P145 was represented by 180 and 150 g of lamb live weight at L29 for the medium and ad libitum treatments, respectively. Mulvaney et al. (2010) showed that the ad libitum treatment consumed two times the herbage content to produce 1 kg of lamb live weight compared with the medium treatment. The study of Mulvaney et al. (2010) primarily involved single-bearing hoggets and the ad libitum hoggets were heavier at the conclusion of the study and would not need to consume as much herbage during the difficult summer/autumn period. The current experiment indicates that offering herbage masses greater than 1400 kg DM/ha from day 85 of pregnancy until parturition does not lead to an increase in hogget lamb live weight at L29.

Conclusion

Increasing the level of nutrition offered to twin-bearing hoggets from day 85 of pregnancy until parturition increased lamb birth weight but did not lead to an increase in lamb live weight during lactation, lamb survival or hogget live weight at L29. The twin-bearing ad libitum treatment hoggets had similar lamb production efficiency compared with the medium treatment hoggets.

Acknowledgements

The authors would like to acknowledge the financial assistance provided by Meat and Wool New Zealand, Massey University and the C Alma Baker Trust. The author PR Kenyon is partially funded by the National Research Centre for Growth and Development. The technical assistance provided by Dean Burnham and Graeme Poole.