Effect of concentrate supplement and sward height on twin-bearing ewe body condition and the performance of their offspring

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1 Australian Journal of Experimental Agriculture, 2008, 48, CSIRO PUBLISHING Effect of concentrate supplement and sward height on twin-bearing ewe body condition and the performance of their offspring J. I. Kerslake A,C, P. R. Kenyon A, S. T. Morris A, K. J. Stafford A and P. C. H. Morel B A Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. B Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand. C Corresponding author. J.I.Kerslake@massey.ac.nz Abstract. These studies investigated the effects of offering concentrate supplement, from day 102 of pregnancy, to twinbearing ewes grazing a 2- or 6-cm sward, on the condition of the ewe and the performance of their offspring in 2005 and In both years, 80 twin-bearing ewes were randomly assigned to either the 2- or 6-cm sward height pasture treatment from day 70 of pregnancy until parturition. From pregnancy day 102, half of the ewes within each sward height were offered 400 g/ewe. day of concentrate supplement. From day 102 until day 140 of pregnancy, ewes offered the concentrate supplement gained more liveweight then ewes offered pasture only. While supplementation affected ewe liveweight, its effects on lamb birthweight and growth were variable. In 2006, concentrate supplementation within the 6-cm sward height treatment increased (P < 0.05) lamb birthweight from an average of 4.8 to 5.3 kg. In 2005, concentrate supplementation increased (P < 0.05) lamb growth by 20 g/day. These inconsistent and minor production gains are unlikely to be cost effective because of the satisfactory performance of lambs from all other nutritional treatments and the extensive feeding of concentrate supplement. Therefore, feeding 400 g/ewe.day of concentrate supplement from day 102 of pregnancy to twin-bearing ewes on a 2- or 6-cm sward height pasture appears not to be a viable management strategy for commercial sheep farmers. Introduction In New Zealand and Australia, pasture-based sheep feeding systems are relied on to provide sufficient energy to meet the high energy demands of ewes in late pregnancy. The effect that pasture feeding levels in late pregnancy have on lamb production, in terms of lamb birth and weaning weights and ewe reproductive performance, has been investigated within New Zealand (Rattray et al. 1982; Scales et al. 1986; Morris et al. 1993; Morris and Kenyon 2004) and Australia (Holst et al. 1986). Morris and Kenyon (2004) have shown that grazing twin-bearing ewes on a sward height greater than 4 cm offers no nutritional or production advantage as dry matter intake on this sward is unrestricted. However, grazing twin-bearing ewes on a sward height of 2 cm restricts pasture intake and has been shown to have either a negative effect on lamb birthweight (Morris and Kenyon 2004) or no effect (Morris et al. 1993). Twin-bearing ewes grazing both a 2- and 4-cm sward mobilise body reserves and lose condition in late pregnancy (Morris et al. 1993; Morris and Kenyon 2004). This suggests that pasture-only diets under these conditions might be inadequate to meet the nutritional requirements of twin-bearing ewes in late pregnancy. This energy deficient state during late pregnancy could be counteracted through the use of concentrate supplementation. Several studies have looked at the use of concentrate supplements during late pregnancy when pasture availability is low (Hall et al. 1992; Stephenson and Bird 1992; Hall and Holst 1996) and when pasture availability is high (Dawson et al. 2005), with mixed results in production gain. Therefore, the aims of the present studies were to determine the effects of feeding a concentrate supplement to twin-bearing ewes grazing a 2- or 6-cm sward height pasture on ewe and lamb performance over 2 years. Materials and methods The experimental design used for these studies was a 2 2 factorial, which investigated the effect of offering concentrate supplement (no v. yes) during mid to late pregnancy to twinbearing ewes grazing a low or high pasture sward height (2 v. 6 cm) on ewe and lamb performance. These trials were conducted in 2005 and In 2005, 509 mixed-age, multiparous Romney ewes were joined to 47 Romney ram hoggets for a 5-day mating period. Crayon marked ewes were weighed, condition scored (scale 0--5, including half units) (Jefferies 1961) and pregnancy scanned using ultrasound at 49 days from the midpoint of the breeding period (P49). All ewes were grazed as one mob under commercial grazing conditions from the commencement of the mating period until P70. On P70, a total of 80 twin-bearing ewes was randomly selected to be grazed on a 2-cm or a 6-cm pasture sward height. Previous research has shown that from P70 ewe intake is unrestricted on a minimum sward height of 4 cm and restricted when grazing a sward height of 2 cm (Morris and Kenyon 2004). By grazing the ewes on these two different sward heights, the production effects of offering concentrate to ewes on restricted and unrestricted grazing conditions were able to be examined. Ewes were balanced for ewe liveweight and condition score and were set-stocked in paddocks with an average size of 1.7 ha and at an average rate of 10 ewes/ha. was offered from P102, as the nutritional requirements of pregnant ewes are highest Ó CSIRO /EA /08/070988

2 Performance of twin-bearing ewes Australian Journal of Experimental Agriculture 989 during the last trimester (Robinson et al. 1999). Half of the ewes within each pasture sward height treatment were either offered 400 g/day of concentrate sheep pellets (Universal stock feed, Harvey Farms Ltd, Wanganui, New Zealand) in two 2.5 m 0.4 m feed bins until average P145 or offered no supplement. An amount of 400 g/day was chosen because offering 400 g/day of concentrate to pregnant ewes grazing low herbage has been previously shown to increase lamb birthweight, while offering 200 g/day has been shown to have no effect (Kenyon et al. 2005). sheep pellets had a dry matter percentage of 90.3%, a crude protein percentage of 14.1% and a metabolisable energy content of 12.3 MJ/kg DM. Ewes were rotated weekly within sward height treatment and concentrate supplement residues were recorded daily. The swards used were at least 4 years old or older and consisted of a mix of ryegrass and white clover. Pasture sward surface heights were measured using a sward stick (Jenquip, New Zealand, 100 readings per paddock) at weekly intervals. If the sward height was found to be below 5 cm in the 6-cm sward height treatment or below 1 cm in the 2-cm sward height treatment, ewes were offered another paddock of appropriate sward height. If the sward height was found to be above 7 cm in the 6-cm sward height treatment or above 3 cm in the 2-cm sward height treatment, additional ewes were introduced to control sward height. Average herbage masses were also measured using a rising plate meter (Ashgrove Pastoral Products, New Zealand, 50 readings per paddock) at 2-week intervals. Liveweight and condition scores of ewes were measured at P70, P102, P116, and P140. A 10-mL blood sample was collected by jugular venipuncture (lithium heparin, Becton, Vacutainer Systems, USA) at P100 and P140. Within 12 h of birth, all lambs were identified to their dam, tagged and their sex and birth rank recorded. Lamb birthweight was also recorded. After 24 h a 10-mL blood sample was collected from the jugular. All animals were then moved to a pasture with a sward height of 6 cm until 52 days after the mid point of lambing (L52). The trial period lasted from March to October Six hundred and eighty Romney, mixed-age, multiparous ewes were joined to seven mature Romney rams for a 17-day breeding period in Rams were fitted with crayon mating harnesses and crayon marks on the ewes were recorded daily as an indicator of mating. On day 70 of pregnancy, 80 twin-bearing ewes were selected to be grazed on a 2-cm and a 6-cm pasture sward height. supplementation was offered to each ewe from P102 up to the day of parturition rather than average day P145 as in Twenty-four hours after parturition all animals were moved to a sward height of 6 cm until 65 days after the midpoint of lambing (L62). The swards used in 2006 had been cultivated and sown with ryegrass and white clover the previous year. All animal measurements were the same as This trial period took place from January to December Blood analysis Ewe plasma samples were analysed using enzymatic assays for glucose (hexokinase method, Roche Diagnostics Ltd, Switzerland) and b-hydroxybuterate (BOH) (Sigma, IL, USA). Lamb plasma samples were analysed for gamma-glutamyl transferase (GGT) using a kit (Roche Diagnostics Ltd, Mannheim, Germany) and glucose, using a hexokinase assay (Roche Diagnostics Ltd). Statistical analysis All ewe and lamb data were analysed by ANOVA in both years with the year effect being nested within the main effects. Ewe liveweight from P70 to P140 was analysed using a repeated-measures analysis (PROC GLM, SAS, SAS Institute, Cary, NC). This model contained the fixed effects of sward height (2 v. 6 cm), concentrate supplementation (no v. yes), time and the interactions between the main effects. Gestation length was fitted as a covariate and retained in the model if statistically significant. Pasture sward height and herbage mass, ewe liveweight gain from P70 to P140, condition score at P70, P100 and P140, ewe plasma glucose and BOH concentrations, lamb birthweight, lamb plasma glucose and GGT concentrations and lamb liveweight gain from birth to weaning were analysed using a general linear model (PROC GLM). The main effects of sward height (2 v. 6 cm), concentrate supplementation (no v. yes) and interactions between these main effects were included in all models. If the interaction was not significant (P < 0.05) then it was removed and the models refitted. In the birthweight and lamb liveweight gain model, sex of the lamb was also used as a fixed effect and gestation length as a covariate. Ewe plasma BOH at P100 and P140, glucose at P140 and GGT activities were not normally distributed and were log-, square- and square-root transformed, respectively, to achieve a normal distribution. The proportion of lambs surviving from birth to weaning was analysed as a binomial trait using the SAS procedure for categorical modelling (PROC GENMOD). Results The average pasture sward heights were kept within the target range (Table 1). The average pasture sward height of the 6-cm sward treatment was greater in 2006 than in 2005 and the average herbage mass for the 2-cm and 6-cm sward treatments was greater in 2005 than In 2005 and 2006, ewes that grazed the 6-cm sward height pasture were heavier than ewes grazed on the 2-cm sward height pasture, on P102, P116 and P140 (P < 0.05; Fig. 1). Supplementation of ewes grazing a 2-cm sward height had a positive effect on ewe liveweight at P140 in 2005 and P116 and P140 in However, supplementation of ewes grazing the 6-cm sward height pasture had no effect on ewe liveweight at P116 or P140 (Fig. 1). Overall, sward height and concentrate supplementation increased ewe liveweight gain from P70 until P140. Ewe liveweight gain was greater in 2006 than in 2005 (Table 2). At P100 and P140, ewes grazing the 2-cm sward had lower body condition scores than ewes grazing the 6-cm sward. supplementation had no effect on ewe body condition score (Table 3). Ewe liveweight at weaning was unaffected by supplementation in both years. In 2006, ewes

3 990 Australian Journal of Experimental Agriculture J. I. Kerslake et al. Table 1. The average sward height (cm) and herbage mass (kg dry matter/ha) of pastures offered to twin-bearing ewes from day 70 of pregnancy until parturition Values are mean s.e. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < Treatment Pasture sward height (cm) Signif. Pasture herbage mass (kg dry matter/ha) Signif cm sward 2.9 (0.17)a 2.8 (0.25)a n.s (55.12)a (58.10)a * 6-cm sward 6.4 (0.15)b 6.9 (0.25)b * (50.32)b (58.10)b **** Ewe liveweight (kg) (a) (b) Period from day 70 to day 140 of pregnancy Fig. 1. The effect of pasture sward height [2 cm (open) v. 6 cm (solid)] and concentrate supplementation [yes (*) v. no(~)] on ewe liveweight (kg) (mean s.e.) at average pregnancy days 70 (P70), 102 (P102), 116 (P116) and 140 (P140) in (a) 2005 and (b) Table 2. The effect of pasture sward height (2 cm v. 6 cm) and concentrate supplementation (yes v. no) on ewe liveweight gain (kg/day) between pregnancy day 70 and day 140 (P70--P140) in 2005 and 2006 Values are mean s.e. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < Liveweight gain from P70--P140 (kg/day) n 2005 n 2006 Signif. 2 cm (0.62)a (0.67)a **** 6 cm (0.62)b (0.70)b **** No (0.62)a (0.67)a **** Yes (0.62)b (0.70)b **** that grazed a 6-cm sward height pasture from P70 until parturition were significantly (P < ) heavier at weaning than ewes grazing a 2-cm sward height pasture during the same period ( kg and kg on a 2-cm v. 6-cm sward height pasture, respectively). At P102, ewes grazing a 6-cm sward height pasture had significantly higher glucose and lower BOH concentrations than ewes grazing a 2-cm sward height pasture in 2005 (glucose, mmol/l and mmol/l on 6-cm v. 2-cm sward height pasture; and BOH, mmol/l and mmol/l on a 6-cm v. 2-cm sward height pasture, respectively) and 2006 (glucose, mmol/l and mmol/l on 6-cm v. 2-cm sward height pasture; and BOH, mmol/l and mmol/l on a 6-cm v. 2-cm sward height pasture, respectively). However, sward height had no effect on ewe plasma glucose and BOH concentrations at P140. Supplementation in both years had no effect on ewe plasma glucose or BOH concentrations at P100. In 2005, supplementation had no effect on ewe plasma glucose concentrations at P140 but reduced ewe plasma BOH concentration at P140 (P < 0.05). This was not observed in In 2005, ewes offered concentrate supplement on a 2-cm sward height pasture gave birth to lighter lambs than ewes offered concentrate supplement on a 6-cm sward height pasture. No other differences in lamb birthweight were observed. In 2006, ewes offered concentrate supplement on a 6-cm sward height pasture gave birth to heavier lambs than ewes on all other nutritional treatments. Lambs born to ewes fed concentrate in 2006 were heavier than lambs born to ewes fed concentrate in 2005 (Table 4). In 2005, lambs born to ewes grazed on a 6-cm sward height pasture had significantly higher plasma GGT concentrations than lambs born to ewes grazed on a 2-cm sward height pasture. In 2006, this effect was reversed. Offering concentrate to ewes in late pregnancy had no effect on lamb plasma GGT concentrations at h of age in 2005 and 2006 (Table 5). had no effect on lamb liveweight gain from birth to weaning in 2005 and In 2005, lambs born to ewes offered concentrate supplement gained 20 g more weight per day than lambs born to ewes that were unsupplemented. This effect of concentrate supplement was not observed in Lamb survival from birth to weaning was not affected by concentrate supplementation or by sward height (Table 6). Discussion These studies investigated the effects of offering concentrate supplement to twin-bearing ewes, grazing either at 2-cm or 6-cm sward height pastures, on ewe liveweight and body condition score and lamb performance.

4 Performance of twin-bearing ewes Australian Journal of Experimental Agriculture 991 Table 3. The effect of pasture sward height (2 cm v. 6 cm) and concentrate supplementation (yes v. no) on ewe condition score (scale 0--5 with 0.5 units) at pregnancy days 70 (P70), 100 (P100) and 140 (P140) in 2005 and 2006 Values are mean s.e. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < Condition score at P70 Signif. Condition score at P100 Signif. Condition score at P140 Signif. n 2005 n 2006 n 2005 n 2006 n 2005 n cm (0.32) (0.35) n.s (0.06)a (0.06)a *** (0.06)a (0.07)a **** 6 cm (0.32) (0.36) n.s (0.06)b (0.07)b **** (0.07)b (0.07)b **** No (0.32) (0.35) n.s (0.06) (0.06) *** (0.07) (0.07) **** Yes (0.36) (0.36) n.s (0.06) (0.07) **** (0.06) (0.07) ****

5 992 Australian Journal of Experimental Agriculture J. I. Kerslake et al. Table 4. The effect of pasture sward height (2 cm v. 6 cm) and concentrate supplementation (yes v. no) on lamb birthweight (kg) h after birth in 2005 and 2006 Values are mean s.e. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < concentrate Lamb birthweight (kg) Signif. interactions n 2005 n cm no concentrate (0.15)ab (0.17)a n.s. 2cm concentrate (0.14)a (0.15)a * 6cm no concentrate (0.14)ab (0.15)a n.s. 6cm concentrate (0.14)bc (0.17)b * Table 5. The effect of pasture sward height (2 cm v. 6 cm) and concentrate supplementation (yes v. no) on lamb plasma gammaglutamyl transferase (GGT) (I/U) at h of age in 2005 and 2006 Values are mean s.e. Data were square-root transformed. Transformed means with s.e. are presented with back-transformed means in parentheses. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < Lamb plasma GGT concentrations (I/U) n 2005 n 2006 Signif. 2 cm (1324.9)a (2550.3)b **** 6 cm (1823.3)b (1849.0)a n.s. No (1383.8) (2143.7) *** Yes (1764.0) (2218.4) n.s. Table 6. The effect of pasture sward height (2 cm v. 6 cm) and concentrate supplementation (yes v. no) on lamb liveweight gain (kg/day) and survival (%) from birth until weaning in 2005 and 2006 Values are mean s.e. Within columns, means followed by differing letters are significantly different at P = Significant differences between years are: *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < Lamb liveweight gain (kg/day) Signif. Lamb survival (%) A Signif. n 2005 n 2006 n 2005 n cm **** (77) (93) * 6 cm * (85) (94) n.s. No a *** (83) (92) n.s. Yes b *** (79) (95) * A Data were logit-transformed, with back-transformed (%) values in parentheses. In both years of this study, ewes grazing a 6-cm sward height pasture from mid to late pregnancy were heavier and in better condition than ewes grazing a 2-cm sward height pasture. Ewe plasma metabolite concentrations at P100 also indicated that less body reserves were being mobilised on the 6-cm sward height pasture. These weight and plasma metabolite differences are likely to be due to having a restricted pasture intake on a 2-cm sward height (Morris and Kenyon 2004). Ewes offered concentrate supplement within the 2-cm sward height treatment were heavier during late pregnancy than ewes that were not fed concentrate supplement. Offering concentrate supplements on a low herbage allowance has previously been shown to have positive effect on ewe liveweight (Stephenson and Bird 1992). However, concentrate supplementation had no effect on the liveweight of ewes grazing 6-cm sward height pastures. Few studies have investigated feeding concentrate supplement in the last trimester of late pregnancy on a high herbage allowance to increase ewe or lamb production. Ewes respond to concentrate supplement on pasture by either eating the concentrate supplement and maintaining or increasing pasture intake (supplementation) or eating the concentrate supplement and substituting pasture intake (Holst et al. 1996). Substitution has been shown to be greater under conditions of high pasture availability or under conditions of low energy demand

6 Performance of twin-bearing ewes Australian Journal of Experimental Agriculture 993 (Dove 2002). Pasture intake in mid to late pregnancy is maximal when grazing a 4--6-cm sward height pasture (Morris and Kenyon 2004) and, therefore, compared with a restricted pasture intake, there should be a smaller energy deficit. It is possible that substitution may have occurred in the 6-cm sward height treatments and that this may explain the lack of difference in liveweight in the supplemented and unsupplemented 6-cm sward height treatment groups. Ewe herbage intakes, however, were not measured and therefore this can only be hypothesised. The lack of difference in birthweights between unsupplemented ewes grazing 2- and 6-cm sward heights is in agreement with Morris et al. (1993) but conflicts with Morris and Kenyon (2004). In the study of Morris and Kenyon (2004) ewes were in a poorer condition compared with the ewes used in Morris et al. (1993) and the present study. Ewe body condition scores in the Morris and Kenyon (2004) study were on average 2.4 units (scale 0--5, with 0.5 units) compared to an average of 2.7 units in Morris et al. (1993) and the present study. The differences in lamb birthweight between experiments may, therefore, be explained by the amount of body reserves available to compensate for a lack of nutrition. If twin-bearing ewes are in relatively good condition, they will have more body reserves to utilise and will cope better than ewes in a poorer condition that are grazing a 2-cm sward height pasture. This should be taken into account when management decisions are made. In 2006, offering concentrate supplement on a 6-cm sward height pasture increased lamb birthweight. In 2005, this was not the case. The different effects of concentrate supplement within the 6-cm sward height pastures in 2005 and 2006 might be explained by the timing of supplementation. In 2005, all ewes were offered concentrate until 140 days after the midpoint of breeding compared with ewes offered concentrate until parturition in Therefore, fetal growth may have been influenced by the extended provision of concentrate during late gestation. If this was the case, however, heavier birthweights in lambs born to the ewes offered 2-cm concentrate in 2006 would have been expected. Pasture quality measurements were not taken between years thus it is not known if pasture quality was different. Although an increase in birthweight was observed in 2006, lambs born to the unsupplemented 6-cm sward height treatment were within the optimal birthweight range (Dalton et al. 1980). Therefore, an increase in lamb survival based solely on lamb birthweight may not be expected. Indeed, no increase in lamb survival was observed in Lamb liveweight gain from birth to weaning was not affected by the herbage allowance fed to ewes during pregnancy. This is supported by the results of Morris and Kenyon (2004). However, in 2005, lambs born to supplemented ewes gained ~20 g/day more liveweight than lambs born to ewes offered pasture only. This was not observed in 2006 but similar results to the 2005 results have been reported by Dawson et al. (2005). The differences in lamb liveweight gain may be explained by the positive relationship found between nutrition in late pregnancy and milk production (Treacher 1970). The differences in ewe liveweight between treatment groups, and the lack of differences in lamb birthweight, suggests that nutrients may have been partitioned towards the ewes for mammary development or to prevent body condition loss rather than fetal growth. This may have a positive effect on milk production in early lactation and on lamb growth from birth to weaning (Morgan et al. 2007). Supplementation has been shown to have a positive effect on colostrum let down (Banchero et al. 2007), although in this study, where lamb plasma GGT concentrations were used as an indirect measure of colostrum intake, no differences were found. Supplementation of ewes on a 2-cm sward height pasture for an extended period in late pregnancy failed to consistently affect lamb birthweight and growth. Even when production effects were observed in the lambs, the size of the response would suggest the treatments are not cost effective. The negative effect of a 2-cm sward on lamb birthweight reported in the literature was not apparent in 2005 or It is possible that this was not observed due to the ewes being in a better condition than in previous experiments. Acknowledgements The authors thank Meat and Wool New Zealand for providing financial support for this research program and the National Research Centre for Growth and Development for the personal financial assistance of the first author. 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