Effect of nutrition during pregnancy on hogget ...

New Zealand Journal of Agricultural Research

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Effect of nutrition during pregnancy on hogget pregnancy outcome and birthweight and liveweight of lambs P. R. Kenyon , S. T. Morris , D. L. Burnham & D. M. West To cite this article: P. R. Kenyon , S. T. Morris , D. L. Burnham & D. M. West (2008) Effect of nutrition during pregnancy on hogget pregnancy outcome and birthweight and liveweight of lambs, New Zealand Journal of Agricultural Research, 51:2, 77-83, DOI: 10.1080/00288230809510437 To link to this article: http://dx.doi.org/10.1080/00288230809510437

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New Zealand Journal of Agricultural Research, 2008, Vol. 51: 77-83 0028-8233/08/5102-0077 © The Royal Society of New Zealand 2008

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Effect of nutrition during pregnancy on hogget pregnancy outcome and birthweight and liveweight of lambs

P. R. KENYON S. T. MORRIS D. L. BURNHAM D. M. WEST Institute of Veterinary Animal and Biomedical Sciences Massey University Private Bag 11222 Palmerston North 4442, New Zealand

Abstract The effect of nutrition during pregnancy in hoggets has not been thoroughly examined under pastoral conditions in New Zealand. The aim of the present study was to determine if a high liveweight gain in pregnancy reduced hogget reproductive performance, and to determine the effect of this regimen on the liveweight of the hogget and her progeny in lactation. Mated, synchronised hoggets, from day 5 of pregnancy, were managed to either: gain 100 g/day in total liveweight throughout pregnancy (Medium), gain 100 g/day until day 36 of pregnancy followed by 200 g/day for the remainder of pregnancy (Medium/High) or to gain 200 g/day throughout pregnancy (High). Actual average daily liveweight gains for Medium and High group hoggets were 134.3 and 223.7 g/day respectively. Average liveweight gains of Medium/High hoggets for the two periods were 103.3 and 237.2 g/day respectively. Significantly (P < 0.05) fewer High hoggets held to service compared to their Medium and Medium/ High counterparts (54.5 versus 78.2 versus 83.6% respectively). However, pregnancy scanning showed that there was no difference between groups in percentage pregnant (48.2 versus 44.5 versus 50.9% respectively), nor were there any differences in the percentage which lambed (44.6 versus 41.2 versus

A07057; Online publication date 6 June 2008 Received 26 July 2007; accepted 8 April 2008

48.3% respectively). Within birthrank there was no effect of hogget treatment on lamb birthweight. In late lactation, not only were lambs born to High hoggets significantly (P < 0.05) heavier than those born to Medium hoggets (17.69 versus 15.88 kg), the hoggets themselves were heavier (54.68 versus 47.80 kg respectively). These findings suggest that farmers should not avoid relatively high liveweight gains in pregnancy with hoggets. In fact, they may be beneficial. Keywords ewe lamb; hogget; lamb birthweight; nutrition; pregnancy; sheep

INTRODUCTION The main reason given by New Zealand farmers for not breeding hoggets (ewe lambs 8-9 months of age) is the perceived impact on two-tooth (18 month) liveweight and thus reproductive performance (Kenyon et al. 2004a). To avoid negative impacts on two-tooth liveweights farmers might choose to offer ad libitum feeding to hoggets throughout pregnancy. However, Wallace et al. (1996, 1997) and Wallace (2000) using a concentrate diet, reported that high total liveweight gains (200-350 g/day), beginning immediately post-embryo-transfer, increased foetal loss and decreased lamb birthweight. This would suggest New Zealand farmers should avoid "high" levels of nutrition during pregnancy. However, under pastoral grazing conditions, Morris et al. (2005) reported that a "high" liveweight gain treatment had no negative effects. In that study the treatments used did not begin until 25 days after the beginning of the breeding period. Conversely, Mulvaney et al. (in press) in a study where feeding regimens began 2 days after breeding, reported higher rates of pregnancy loss in hoggets which had "high" total liveweight gains compared to those with "moderate" gains. This later result combined with those of Wallace et al. (1996) suggest that "high" total liveweight gains in early pregnancy is responsible for increased pregnancy loss in hoggets. Therefore,

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New Zealand Journal of agricultural Research, 2008, Vol. 51

the aims of the present study were to firstly determine if "high" total liveweight gains beginning in early pregnancy caused poor reproductive performance in hoggets, and secondly to determine the effects of differing total liveweight gains during pregnancy on the performance of the hogget and her offspring in lactation.


MAterIAls And M e t h o d s experimental design and animals The study was conducted at Massey university's Keeble Farm, 5 km south of Palmerston North, New Zealand. The experimental design was a 3 x 2 factorial, incorporating: three liveweight gain treatments ("Medium" versus "Medium/high" versus "high") and two pregnancy ranks (single versus twin). Three hundred and forty-nine Romney ewe hoggets (8-9 months of age) were selected from a commercial flock of 422 hoggets on the basis they had been mated during a 4-day breeding period. all hoggets had been synchronised via a CiDR (Pharmacia & upjohn, New Zealand; 0.3 g progesterone). The trial period was from May 2005 (breeding) to December 2005 (weaning). treatments Five days after CiDR removal (one day after the end of the 4-day breeding period, P5) hoggets were randomly allocated to one of three total liveweight gain treatments. approximately a third were managed with the aim of achieving a 100 g/day gain in total liveweight during pregnancy (Medium, n = 119), a third with the aim of achieving a 100 g/day increase during the period P5 to P36 followed by a 200 g/day increase for the remainder of pregnancy (Medium/high group, n= 116) and the remainder with the aim of achieving a gain of at least 200 g/day throughout the entire pregnancy period (high group, n= 112). During the period P5 until P36 Medium and Medium/high hoggets were managed as one group with the high hoggets managed as a separate group. From P37 until parturition the Medium/high and high hoggets were managed as one group with Medium hoggets managed separately. hoggets were weighed approximately fortnightly and based on the results of these weights, adjustments were made to grazing area to ensure target total liveweight gains were achieved. During the period P7 until P36, five crayon harnessed vasectomised (teaser) rams were

introduced into each group of hoggets. a t the end of this period the teasers were removed and crayon marks recorded. a l l hoggets which had been crayon marked were assumed to have returned to service and were removed for the remainder of the study. hoggets which did not return to service to the teaser rams were pregnancy scanned via ultrasound at P53 and diagnosed as either nonpregnant, single- or twin-bearing. Non-pregnant hoggets were then removed from the remainder of the study. Within 24-36 h of parturition all hoggets and their lambs were moved into a new paddock and merged into one flock group until weaning (68 days after the mid-point of the lambing period, L68). Animal measurements hoggets were weighed within 1 h of removal from pasture on P0, P15, P36, P79, P102, P129, P143 and L68. The gestation length was calculated based on the number of days between mating date (based on daily crayon mark readings during the synchronised breeding period) and parturition. ewes with lambs still present at L68 were shorn and their fleece weights recorded. All lambs were identified to their dam, tagged, sexed, recorded for birth-rank, weighed and had their girth, crown rump length (CRL), front left leg (FL) and hind left leg (hL) measured within 12 h (L0) of birth, regardless of category (dead versus alive). Liveweights of lambs were also recorded at L39 and L68. The Massey university animal ethics Committee approved all procedures used in this study. statistical analysis a l l measurements on hoggets and lambs were subjected to analysis of variance using the statistical package Minitab (1998) unless otherwise stated. The main effects of pregnancy rank (or birth-rank) and nutritional treatment and interactions between these parameters were included in the original models. all non-significant (P > 0.05) interactions were then removed and the models re-fitted. Birth-rank or rearing-rank of the lamb or ewe in the lactation period did not change if one twin from a pair died before weaning. in the models used to partition variation in lamb liveweight, sex of lamb was used as a fixed effect. in the models used to partition variation in crown rump length, girth, forelimb and hind limb length, date of birth was used as a covariate.

Kenyon et al.—Nutrition during pregnancy and hogget pregnancy Fig. 1 The effect of hogget treatment on total liveweight change in hoggets during pregnancy.

79

80 -,

70 -

en

40 A »—•

Medium Medium/High High


30 0 20

40

60

80

100

120

140

Day of pregnancy

The percentage of hoggets that did not return to service, were diagnosed pregnant, or that lambed were analysed as binomial traits using the SaS (2005) procedure for categorical data modelling (GeNMoD).

RESULTS Hogget liveweights and fleece weights "high" group hoggets were heavier (P < 0.05) than both Medium and Medium/high hoggets from P15 until P143 (Fig. 1). Medium/high group hoggets were heavier (P < 0.05) than Medium hoggets at P129 and P143. average daily liveweight gains for Medium and high group hoggets from P0 to P143 were 134.3 and 223.7 g/day respectively. average liveweight gains of Medium/high hoggets for the period P0 to P36 and P37 to P143 were 103.3 and 237.2 g/day respectively. Throughout pregnancy, twin-bearing hoggets were heavier (P < 0.05) than their singleton counterparts (by 1.5-4.0 kg, data not shown). a t L68 high hoggets were heavier (P < 0.05) than their Medium counterparts but neither group differed from Medium/high hoggets (Table 1) although Medium/high hoggets tended (P = 0.08) to be heavier than Medium hoggets.

The fleece weights of High hoggets were heavier (P < 0.05) than that of both Medium/high and Medium hoggets by approximately 0.5 kg (Table 1). The fleece weights of single- and twin-bearing hoggets did not differ. Hogget reproductive performance A greater (P < 0.05) percentage of high hoggets returned to service to teaser rams in the 31 days after the breeding period (Table 2). however, at pregnancy diagnosis (P53) there was no difference in overall pregnancy rates between the three groups, nor was there a difference in the percentage that lambed. Those identified as non-pregnant at pregnancy diagnosis tended (P = 0.06) to be lighter at P1 than those identified as single-bearing (37.3 ± 0.05,38.62 ± 0.3), and were lighter (P < 0.05) than twin-bearing hoggets (41.43 ±0.81 kg). The gestation lengths of Medium fed hoggets was significantly longer (P < 0.05) than that of both Medium/high and high fed hoggets, by approximately 1 day (Table 1). Gestation lengths of single and twin bearing ewes did not differ. Lambs There was an interaction (P < 0.05) between hogget treatment group and birth-rank on lamb birthweight such that twin lambs born to Medium hoggets were lighter (P < 0.05) than their single-born counterparts

New Zealand Journal of agricultural Research, 2008, Vol. 51

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table 1 The effect of pregnancy rank and hogget treatment on hogget gestation length (days), liveweight (kg) at L68 and fleece weight at L80 (mean ± SE). Means within treatments with letters in common or no superscripts are not significantly different (P > 0.05). L68, L80 = 68 and 80 days respectively after parturition. Gestation length n


Pregnancy rank 1 2 Treatment Medium Medium/high high

hogget liveweight at L68 n

Fleece weight n

135 21

145.3 ±0.17 144.9 ± 0.43

96 18

52.65 ± 0.74 51.02 ±1.78

96 18

4.30 ± 0.07 4.09 ±0.16

49 57 50

145.8b ±0.32 144.6a ±0.33 144.8a ± 0.32

38 39 37

47.80a ±1.44 53.03ab ±1.91 54.68b ±1.61

38 39 37

3.95a ±0.12 4.07a ±0.13 4.57b ±0.13

table 2 The effect of hogget treatment on the percentage of hoggets that held to first service, were diagnosed as pregnant at P53 and that lambed. Values presented are logit transformed (means ± SE) and numbers in parentheses are back-transformed percentages. Means within treatments with letters in common or no superscripts are not significantly different (P > 0.05).

Treatment Medium Medium/high high

n

Percentage that held to first sevice

Percentage diagnosed pregnant

Percentage that lambed

119 116 112

-1.27 1 ±0.22 a (78.2 2 ) -1.63 ±0.25 a (83.6) -0.18 ±0.19 b (54.5)

0.21 ±0.18 (44.5) 0.03 ±0.19 (50.9) 0.07 ±0.19 (48.2)

0.36 ±0.19 (41.2) 0.07 ±0.19 (48.3) 0.22 ±0.19 (44.6)

1

Logit transformed. Back-transformed (%).

2

table 3 The effect of birth rank and hogget treatment on lamb liveweight (kg) at birth (L1), L39 and L68 (mean ± SE). Means within treatments with letters in common or no superscripts are not significantly different (P > 0.05). Liveweight L1 n Birth rank Single Twin

L39 n

L68 n

135 42

4.36a ±0.08 3.62b ±0.15

97 29

13.37b ±0.24 10.95a ±0.43

96 30

18.72b ±0.32 15.05a ±0.57

Treatment Medium Medium/high high

58 61 58

4.02 ±0.13 3.74 ±0.17 4.21 ±0.14

44 43 39

11.50a ±0.37 12.21ab ± 0.39 12.78b ±0.39

43 42 41

15.88a ±0.49 17.08ab ±0.53 17.69b ±0.51

Br × Treatment1 Single × Medium Twin × Medium Single × Medium/high Twin × Medium/high Single × high Twin × high

40 18 53 8 42 16

4.68 c ±0.14 3.37a ±0.22 4.19bc ±0.12 3.29ab ±0.31 4.20bc ±0.14 4.22abc ± 0.24

1

Birth rank by dam treatment interaction.

Kenyon et al.—Nutrition during pregnancy and hogget pregnancy (Table 3). however, in both the Medium/high and high groups birthweights of single- and twin-born lambs did not differ. hogget group had no effect (P > 0.05) on lamb girth, CRL, FL and hL. a t both L39 and L68 lambs born to high hoggets were heavier (P < 0.05) than those born to Medium hoggets. Those born to Medium/high hoggets did not differ in liveweight to those born to either Medium or high hoggets.


dIscussIon This study set about to achieve high liveweight gains in pregnancy to determine if this would reduce reproductive performance of hoggets. The target total liveweight changes were achieved with the high treatment regimen hoggets under ad libitum feeding conditions achieving 223 g/day. Similarly Morris et al. (2005) and Mulvaney et al. (in press) achieved total liveweight gains of approximately 210 and 230 g/day respectively in their ad libitum feeding groups. These combined results would suggest a total liveweight gain of approximately 230 g/day for the entire pregnancy period may be near the maximum achievable for pregnant hoggets under pastoral grazing conditions. all hoggets in the present study had displayed evidence of breeding, via the presence of crayon harness marks before group allocation. it is apparent that more of the high treatment hoggets were crayon marked by the vasectomised rams during the 31-day period post-breeding than either the Medium or Medium/high hoggets. This would suggest that either conception rates were lower and/or embryonic loss higher in the high group, although this is unknown. McMillan & McDonald (1983) and Wallace et al. (1996) have both reported a negative relationship between level of nutrition and conception rates in hoggets. Mulvaney et al. (in press) reported lower pregnancy rates in high liveweight gain hoggets compared to their moderate liveweight gain counterparts. Further, in mature ewes high liveweight gains post-breeding were associated with lower maternal progesterone concentrations, and it is known that lower progesterone concentrations can result in lower embryo survival rates (Parr et al. 1982,1993). interestingly, by pregnancy diagnosis 48 days after the end of the breeding period, there was no difference in the pregnancy rates between the three regimens in the present study. Wallace et al. (1999) and Morris et al. (2005) have previously reported no

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effect of hogget growth on pregnancy rate. The lack of a difference in pregnancy rates but high return to service rates suggests one of two outcomes must have occurred. either Medium and Medium/high hoggets lost a greater percentage of pregnancies post-vasectomised ram removal, or a more likely explanation is that many hoggets in the Medium and Medium/high group did not conceive to the progesterone induced synchronised breeding, but then failed to return to service, while those that failed to conceive in the high treatment were more likely to return to service. Quirke (1979a,b) and McMillan & McDonald (1983) found that up to 86% of ewe lambs which failed to conceive to a breeding did not return to service. Quirke (1979b) stated that more than half of those that failed to return to service had lapsed into anoestrus. Given that liveweight within breed is a major factor controlling attainment of puberty (Dyrmunsson 1973) it is possible that the heavier weights achieved during the 31 days postsynchronised breeding in the high hoggets resulted in a greater proportion of these animals displaying oestrus after they failed to conceive. The apparent anomaly warrants further study. in the present study foetal loss could only be examined between pregnancy diagnoses and lambing. it is apparent that there was no difference in pregnancy loss rates between the three treatment groups. This supports the findings of Morris et al. (2005), but contrasts with the findings of Mulvaney et al. (in press) under pastoral conditions and Wallace et al. (1996) and Wallace (2000) under housed conditions. Mulvaney et al. (in press) hypothesised that the potential conflict between their results and those of Morris et al. (2005) might be due to the later onset of the nutritional regimens in the later study. however, the timing of the start of the liveweight change regimens in the present study was similar to that of Mulvaney et al. (in press) and the growth rate changes appear to be greater in the present study. Therefore the apparent difference between studies is difficult to explain. Low birthweights can be associated with higher rates of postnatal loss in lambs (McMillan 1983). in the present study, birthweight was not reduced by high liveweight change as reported by Wallace et al. (1997,2003). The present finding supports the lack of difference in birthweight of lambs born to moderate and high liveweight gain treatments in the studies of Morris et al. (2005) and Mulvaney et al. (in press). Weight of lambs weaned is a further important measure of reproductive success in hoggets. heavier


New Zealand Journal of Agricultural Research, 2008, Vol. 51 lambs at weaning offer more options to farmers as they could be sold directly for slaughter, have a higher store value or potentially, higher growth rates allow for earlier weaning. Morris et al. (2005) and Mulvaney et al. (in press) reported lighter weaning weights in lambs born to hoggets that had relatively poor liveweight gains in pregnancy. In the present study, lambs born to the Medium group were lighter at weaning than their counterparts. Liveweight at breeding in hoggets is positively related to lamb growth in hoggets (Kenyon et al. 2006). Further, in mature ewes, pre-lambing liveweight is positively related to lamb growth (McCall et al. 1986; Kenyon et al. 2004b). Peak m ilk production and total m ilk yield in m ature ewes is affected by pregnancy nutrition (Treacher 1970; Dove etal. 1988) with body reserves being able to be mobilised for milk production to enhance lamb growth.

in the Medium group ewes. Liveweight at 18-month breeding is known to effect reproductive performance (Kenyon et al. 2004c).

Liveweight of the young dam at weaning is an important consideration with hogget lambing. It is known that two-tooth liveweight positively affects breeding performance (McMillan & MacDonald 1983). The lighter liveweights of the Medium hoggets suggest that they are more likely to display poorer two-tooth breeding compared to their counterparts. Morris et al. (2005) and Mulvaney et al. (in press) reported similar relationships between liveweight regimens in pregnancy and weaning weight. The heavier fleece weights in the High group hoggets support the findings of Morris et al. (2005). Liveweight gains of 100 and 200 g/day in 40 kg ewe hoggets require approximately 5.2 and 10.4 MJ ME/day above maintenance requirements (Nicol & Brookes 2007). Therefore, some consideration to the additional feeding costs in relation to potential productive gains should be given. There were no differences in reproductive performance or liveweights at weaning of hoggets or lambs between the Medium/High and High treatment groups. Therefore, the data may suggest that the High group would be less economic than the Medium/High group and that farmers could consider liveweight gains of only 100 g/day in early pregnancy, followed by higher liveweight gains. Economic effects of the lower liveweights at weaning of Medium group hoggets and their lambs, in comparison to the High group are difficult to quantify as these depend on value of the lambs and the cost of the additional feed required to ensure suitable 18-month breeding weights are achieved

ACKNOWLEDGMENTS

CONCLUSION The high total liveweight gains in the present study failed to reduce pregnancy rates at scanning or foetal loss post-scanning. In contrast, the higher liveweight gains were associated with increased hogget and lamb liveweights at weaning. Therefore, these results would suggest that high liveweight gains of approximately 200 g/day in pregnancy under pastoral grazing conditions should not be avoided, and may be beneficial.

The authors thank Massey University and Meat and Wool New Zealand for financial support for this research programme.

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Kenyon et al.—Nutrition during pregnancy and hogget pregnancy


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