Effect of supplementation with rumen undegradable protein on milk production and ovarian activity in double purpose cows

Abstract

In order to evaluate the effect of ruminal undegradable protein (RUP) supplementation on the productive and reproductive performance of double purpose cows, 20 cows (F1 Holstein×Brahman) at 4 days postpartum (body weight 420±24 kg) were divided in two groups (n=20) to receive 2 kg/animal/day of 30% RUP or 45% RUP supplement for 100 days. Cows were weighed, the body condition score (BCS) was recorded weekly and milk production and composition was evaluated twice a week. Faeces, concentrate and pasture samples were collected to estimate forage intake and digestibility. Assessments of oestrous behaviour were performed by visual observation from Day 14 until Day 105 postpartum and blood samples were collected twice a week to measure progesterone. The results show that the use of 45% RUP did not improve intake, digestibility, milk production and composition, body weight or BCS (P > 0.05), but tended to reduce (P = 0.15) the number of days to first normal luteal activity and increased (P=0.14) the number of animals with luteal activity in the first 105 days postpartum. It is concluded that supplementation with 45% RUP did not improve forage use or milk production, but had a positive effect on the restoration of ovarian activity in double purpose cows in early postpartum.

Keywords:

• RUP
• luteal activity
• milk production
• BCS
• DMI
• digestibility

Introduction

The productive and reproductive performance in cattle under tropical conditions is affected negatively by low forage availability and quality, which make the use of energy and protein supplements important to mitigate negative effects (Lents et al. 2008). The low productive or reproductive response in postpartum cows is associated with low forage digestibility or low intake of amino acids (AA), which cause a mobilisation of adipose and muscle tissue (Baumann et al. 2004).

The effect of energy supplementation on productive and reproductive responses in cattle has been reviewed widely and has shown positive effects (Keady et al. 2001; Funston 2004; Cavestany et al. 2009), while the effects of protein supplementation have been inconsistent because of the differences in protein degradability of the supplements and forages. It has been thought that, however, supply of protein to cattle in tropical areas may have important potential because it improves forage digestibility and energy utilisation by increasing the AA supply for the animal (Gilbery et al. 2006). In postpartum dairy cows, increasing ruminal degradable protein (RDP) from 11.1 to 15.7% reduced the days to first ovulation (Garcia-Bojalil et al. 1998a); however, excess RDP can reduce milk production and intake (Garcia-Bojalil et al. 1998b). Supplementation with RDP increases VFA production and the duodenal flux of microbial protein, which may explain the positive effect of RDP (Wickersham et al. 2008). Nevertheless, in beef cows fed with moderate-quality hay, the use of 22% ruminal undegradable protein (RUP) did not affect the body weight, BCS, milk production or composition in comparison with 4.2% RUP (Encinias et al. 2005); however, an increase in RUP in cows decreases the duration of the postpartum period (Kane et al. 2004).

It has been reported that supplementation with RUP can improve the digestibility of low quality forages and increase protein flow to the duodenum. In steers fed with hay that contained 6.0% crude protein, supplementation with 0.8, 19.6 or 41.6% RUP increased total organic matter digestion compared to unsupplemented hay (Reed et al. 2007). Heifers fed with a diet that contained 28% RUP tended to increase body weight and had improved metabolisable protein in comparison with heifers fed a diet with 14% RUP (Patterson et al. 2003). Based on this evidence and given that tropical forages generally contain small amounts of protein (Alonso et al. 2008), we hypothesised that the use of a supplement greater in RUP would positively affect the reproductive performance in postpartum double purpose cows under conditions of the humid tropics of México by improving intake and forage digestibility. Thus, the objective of the present experiment was to compare two supplements with 30 and 45% RUP on the reproductive response in postpartum double purpose cows and the effects on forage consumption and digestion.

Material and methods

Animal management and treatment

The experiment was conducted on a private farm located at 17°41′24″ north latitude and 91°43'6″ west latitude in Chiapas, México. The climate is warm and humid with a mean annual temperature of 26.6°C and 2335.9 mm of rainfall. Twenty postpartum cows of double purpose (F1 Holstein×Brahman) with a body weight of 420±24 kg, body condition score (BCS) of 2.7±0.19 and 4 days postpartum were used. Cows were grazing in Brachiaria decumbent during the period after milking and randomly divided into two groups for treatments. The 30RUP-treated group received a supplement containing 30% RUP once daily (2 kg/animal/day; Table 1) whereas the 45RUP-treated group received the same amount of supplement but with 45% RUP (Table 1). Both groups received the supplement from Days 4 to 105 postpartum and it was provided to individual animals in the morning (06:30 h) at milking time. Cows were milked once daily in the morning by an automated machine; calves were used to stimulate milk ejection prior to the cow's entrance into the milking station. During this period, the calves could suckle one udder quarter. The calves were isolated later in the morning and at approximately 14:00 h, a second suckling was allowed during the first 3 months after birth.

Table 1. Ingredients and chemical composition of the supplements used from Day 4 to 105 postpartum in double purpose cows with different concentrations of rumen undegradable protein (RUP).

	Supplement
Ingredient	30% RUP^d	45% RUP^d
Galmez®^a	87.4	44.39
Proavit®^b	–	13.50
Enervit®^c	–	1.50
Sorghum grain	–	29.78
Chemical composition (%)
Dry matter	87.42	87.95
Crude protein	15.79	16.06
Rumen undegradable protein	31.00	46.00
Neutral detergent fibre	25.37	31.49
Acid detergent fibre	11.28	18.31
Ether extract	3.28	1.23
Nitrogen extract free	3.28	1.23
ME (Mcal/kg DM)	3.66	3.32
Ca	0.94	2.67
P	0.39	1.43
^aEnergy concentrate produced by Zuavit S.A. de C.V. Ecatepec de Morelos, State of México.
^bProtein concentrate produced by Granos y Alimentos del Mezcalapa de C.V. Huimanguillo, Sate of Tabasco.
^cRuminally protected fat produced by Zuavit S.A.de C.V. Ecatepec de Morelos, State of México.
^dEstimated by ruminal incubation (12 h).

Reproductive evaluation

Cows were checked by rectal palpation weekly to evaluate for the presence of corpus luteum in the ovary from Days 4 to 105 postpartum. Oestrous behaviour was detected by visual observation twice daily (6 and 18 hours) from Day 14 to the end of the experimental period, to determine the interval from calving to first oestrus. Additionally, blood samples were collected by jugular venipuncture twice a week to determine the interval from calving to first normal luteal activity. Samples were placed on ice immediately after collection and centrifuged at 3000 g for 30 min. Plasma was decanted into polypropylene tubes and stored at −20°C until further analysis. Progesterone in plasma was measured by radioimmunoassay in the solid phase (Coat-A-Count, Diagnostic Products Corporation). The coefficients of variation for the low doses were 8.4 and 8.3% for intra- and inter-assay, respectively, whereas those for the high doses were 1.2 and 1.6% for the intra- and inter-assay coefficients, respectively. The duration of the luteal phase was considered when progesterone concentrations were >1 ng/mL (Zalesky et al. 1984).

Feed intake and digestibility evaluation

In both groups over a 15-day period, a dose of 3 g of chromic oxide/animal/day was administered with a device used for intra-ruminal capsule delivery to estimate the digestibility and dry matter intake (Alonso et al. 2008). In the last 5 days of chromic oxide administration, faecal grab samples were collected, dried at 60°C for 48 h and stored until later analysis. The chromic oxide concentration was measured using a spectrophotometer as described by Williams et al. (1962) after drying the sample at 600°C for 2 h and then digesting it with a solution containing manganese sulphate and phosphoric acid at 85% followed by a solution of potassium bromide at 4.5%; calcium solution was added to record the absorbance. Samples from pastures and supplements were collected to determine acid-insoluble ash as an internal marker (Keulen and Young 1977), which basically involved incineration of the sample (450°C, 5 h) followed by digestion with HCl (2 N) to obtain acid insoluble ash as a residue. This evaluation was performed three times throughout the experimental period, at postpartum Days 35, 75 and 105. Dry herbage intake and digestibility were calculated as described by Geerken et al. (1987) and Aranda et al. (2001). Since the acid insoluble ash in the faeces originated from two feeds (supplement and forage), the intake of forage could be estimated because the daily intake of the supplement was recorded using the following equation with the total faecal output and the faeces produced from the supplement:

Where (AIAf) = acid-insoluble ash in faeces (g/kg DM), TFO = total faecal output obtained with Cr₂O₃ as an external marker (g/d DM), (AIAs), acid-insoluble ash in protein supplement (g/kg DM), DSI = daily supplement intake (g/DM), (AIAg) = acid- insoluble ash in grass (g/kg DM).

Productive evaluation

Body weight and BCS were scored weekly to assess changes across the experimental period. Milk production was recorded twice a week and milk composition was evaluated by a red light spectrophotometer (Milko-tester Minor A/A N; Foss Electric Denmark®).

Statistical analysis

The results for digestibly, intake, milk production, body weight, BCS, days to first oestrous and days to first luteal activity were analysed using PROC GLM (SAS Institute 1999) with the 30RUP and 45RUP groups as treatments. The percentage of cows with luteal activity during the experimental period were analysed by the Chi-square test using JPM 5.0.1 software. Because treatment×period interactions were not significant for the concentrate, forage digestibility and dry matter intake, the data were averaged.

Results and discussion

Means for intake and digestibility of the concentrate and forage are shown in Table 2. The use of 30 or 45% RUP did not affect the intake or digestibility of concentrate and forage during the experimental period. In contrast, in beef cows fed bromegrass hay, the use of a supplement with 22% RUP increased the forage and total dry matter intake (DMI) in comparison with cows receiving a supplement with 4.2% RUP (Encinias et al. 2005). In dairy cows supplemented with three amounts of RUP (4.5, 14.9 and 29.1% of DMI) during the postpartum period, there were no differences in DMI, but the apparent digestibility was increased with greater amounts of protein (Wright et al. 1998). In beef steers supplemented with different amounts of RUP (5.3, 22.3 and 41.2% RUP/kg supplement), digestion was increased by RUP supplementation (Sletmoen-Olson et al. 2000a).

Table 2. Intake and digestibility of concentrate and forage in double purpose cows which received two different amounts of rumen undegradable protein (RUP).

	Treatment
	30% RUP (n=10)	45% RUP (n=10)	SEM	P value
Concentrate intake (kg/day)	1.3	1.1	0.08	0.16
Forage intake (kg/day)	8.5	9.2	0.6	0.47
Total dry matter intake (kg/day)	9.8	10.3	0.6	0.52
Concentrate dry matter digestibility (%)	84.2	84.4	1.9	0.80
Forage dry matter digestibility (%)	43.3	44	0.6	0.83
Total dry matter digestibility (%)	51.5	52.3	2.3	0.80
SEM = Standard error of means.

Cows in the 45% RUP group started the experiment with greater body weight (P<0.05) than cows in the 30% RUP group and obviously finished the experiment with greater body weight. However, the change in body weight, BCS and milk fat did not differ between groups (Table 3). The average milk production and milk fat was not affected by the amount of RUP in the supplement (Table 3). The reproductive performance of the cows during the experimental period is summarised in Table 4. The interval from calving to first oestrus and the period to first luteal activity were not different between groups, while the interval from parturition to first normal luteal activity (P=0.15) and the percentage of animals with luteal activity (P=0.14) during the experimental period tended to be improved in the 45% RUP-treated group compared to the 30% RUP-treated group. Milk production, milk fat and BCS were not different between the groups; however, body weight was greater in the 45% RUP-treated group.

Table 3. Milk production, body weight and body condition score in double purpose cows which received two different amounts of rumen undegradable protein (RUP).

	Treatment
	30% RUP (n=10)	45% RUP (n=10)	SEM	P value
Milk production to sale (kg/day)	4.20	4.61	0.25	0.26
Fat milk (%)	2.10	2.28	0.13	0.35
Initial body weight	401.0	445.1	13.9	0.037
Final body weight (kg)	375.3	421.5	13.9	0.03
Change in body weight (kg)	−25.7	−23.6	14.0	0.74
Final body condition score (1 to 5)	2.6	2.7	0.19	0.65
SEM = Standard error of means.

Table 4. Reproductive performance in double purpose cows which received two different amounts of rumen undegradable protein (RUP).

	Treatment
	30% RUP (n=10)	45% RUP (n=10)	SEM	P value
First oestrous postpartum (days)	42	45	18.1	0.86
First normal luteal activity (days)	99	82	8.02	0.15
Duration of first normal luteal phase (days)	12	12.8	1.28	0.72
Percentage of cows with luteal activity	10	40		0.14
SEM = Standard error of means

In dairy cows supplemented with 4.5, 14.9 and 29.1% RUP, there was a linear increase in milk production with the increase of RUP and a linear reduction in back fat (Wright et al. 1998). However, the greater amount of RUP in this study was similar to that in the 30% RUP-treated group. In another study with beef cows fed bromegrass hay (9.6% CP) supplemented with 4.2 or 22% RUP for 60 days from postpartum day 41, there was no difference in body weight, BCS, milk production or milk fat at the end of the supplementation period (Encinias et al. 2005). The response to supplementation appears to be influenced by the genetic potential of the cows. The lack of response in double purpose cows could be explained because they are not a specialised milk-producing breed. Evaluations of the levels of RUP with Holstein cows with high or low genetic merit did not show interactions between the RUP level and genetic potential, but demonstrated beneficial effects on production and reproductive performance (Westwood et al. 2000). These interactions could be detected in less cows with genetic potential, such as dual-purpose cows.

The days to first luteal activity tended to be shorter with the supplement that contained 45% RUP than the supplement with 30% RUP, whereas the number of animals with luteal activity during the experimental period also tended to be greater in the 40% RUP-treated group than in the 30%-treated group. In agreement with the reproductive results of this study, beef cows fed a greater amount of RUP (156 g/day) from days 10 to 110 postpartum had a shorter period to first oestrous than animals fed with low RUP (118 g/day). However, the pregnancy rate was not affected by the amount of RUP consumed (Waterman et al. 2006). Contrary to these results, in beef cows receiving three amounts of RUP (5.3, 22.3 and 41.2%) during early lactation, the number of days to first oestrous and rebreeding was not affected in comparison with cows fed with cool-season prairie grass hay with 5.8% CP (Sletmoen-Olson et al. 2000a; Sletmoen-Olson et al. 2000b). Dairy cows fed a supplement with 10.8% RUP from partum to 199 days in milk had a longer interval from calving to first oestrus than cows fed a supplement with 6.1% RUP, even when the amount of crude protein was similar (Chapa et al. 2001). The negative effects of protein supplementation are associated with an increase in N-urea in blood, which affects ovarian follicular and embryo development (Chapa et al. 2001). However, in the present experiment, N-urea levels in the blood were similar between treatment groups (6.64 and 6.51 mg/dL for 30 and 45% RUP, respectively) and there was no negative effect on the postpartum time to first oestrus and the duration of luteal activity. An increase in RUP may increase the supply of AA for intestinal absorption, which may improve the glucogenic potential of the supplement (Waterman et al. 2006) or contribute an essential AA such as methionine, which can improve ovarian function (Alonso et al. 2008).

Even though the use of 45% rumen undegradable protein supplement did not enhance the digestibility of forage or improve milk production, this supplement had a positive effect on restoring ovarian activity in double purpose cows during early postpartum. The results of this experiment imply that it may be advisable to supplement dual-purpose cows with rumen undegradable protein to improve reproductive performance.