Table 9.2 Time elapsed after birth before calves that were born alive attempted to stand, successfully stood and suckled from a heifer for the
CHAPTER 1 0 Maternal plasma oestrone sulphate concentration
prior to parturition in relation to b i rth weight of the calf in primi parous, two-year-old Ang us heifers
Publications arising from this chapter:
Hickson RE, Kenyon PR, Lopez-Villalobos N, Morris ST.
Short communication: Maternal plasma oestrone sulphate concentration prior to parturition in relation to birth weight of the calf in primiparous, 2-year-old, Angus heifers. Animal Reproduction Science 1 14, 30 1 -5, 2009
Abstract
Dystocia and assisted parturition in primiparous heifers are persistent problems in beef herds, and incidence increases with increasing birth weight of calves. Plasma samples taken from 33 primiparous, two-year-old, Angus heifers two days prior to parturition were analysed for oestrone sulphate concentration. Additional samples taken at 4, 6, 8 and ten days prior to parturition were analysed for 1 7 of these heifers. At parturition, birth weight of the calf, post-partum live weight of the heifer, assistance at calving (n=6) and status of the calf (stillborn (n=4) versus alive) were recorded. Maternal plasma oestrone sulphate concentration was stable from ten until four days prior to parturition and increased between four and two days prior to parturition for non-assisted heifers. M aternal plasma oestrone sulphate concentration did not affect the probability of assistance at parturition or stillbirth.
Introduction
The predominant cause of dystocia and assisted calving in primiparous two-year-old beef heifers is feto-maternal disproportion and the most important factor affecting the probability of dystocia is birth weight of the calf (Rice 1 994; Chapters 5, 7 and 9). Birth weight of the calf is related to weight of cotyledons (Echternkamp 1 993; Chapters 5 and 6), probably because cotyledons play a major role in the transfer of nutrients and metabolites between the maternal and fetal units (Shah et al. 2007). Furthermore, synthesis and conjugation of oestrogens occurs in the cotyledons; thus a positive correlation between the metabolic and steroidogenic capacity of the cotyledons and transfer of nutrients from the maternal bloodstream to the fetus would result in a positive correlation between maternal plasma oestrone sulphate concentration and birth weight (Shah et al. 2007) .
Previous studies have indicated that maternal plasma oestrone sulphate concentration i n the ten days prior to parturition was related to birth weight o f the calf (Echternkamp
1 993; Zhang et ai. 1 999a); however, there is conflicting evidence as to the stability of maternal plasma oestrone sulphate concentration during the ten days prior to parturition. Some authors reported that maternal plasma oestrone sulphate concentration did not change in the ten days prior to parturition (Echternkamp 1993; Zhang et al. 1 999a), whereas others have reported variation during this period (Abdo et al. 1 99 1 ; Kornmatitsuk et al. 2004). Zhang et al. ( 1 999a; b) reported a positive correlation
Maternal plasma oestrone sulphate concentration
between neonatal viability and maternal plasma oestrone sulphate concentration, and also observed that the least viable calves had all experienced dystocia at birth, perhaps indicating the existence of a link between maternal plasma oestrone sulphate concentration and dystocia.
The aim of this experiment was to determine whether maternal plasma oestrone sulphate concentration prior to parturition was related to birth weight of the calf. A secondary objective was to determine whether maternal plasma oestrone sulphate concentration varied over the ten days prior to calving in primiparous, two-year-old, Angus heifers.
Materials and Methods
An imals and treatments
Thirty-three primiparous two-year-old Angus heifers were observed at least thrice daily (maximum time elapsed between observations was eight hours) during the parturition period to identify heifers in need of assistance to deliver their calf and to assess the status of the calf at birth (alive or stillborn). Assistance was provided at the discretion of the farm manager, using guidelines that recommended assisting heifers four hours after the onset of parturition. Each heifer had conceived to a single insemination with semen from one of five Angus bulls (BeefPac, LIe, Hamilton, New Zealand) at observed, synchronised oestrus (DO; n=23, or D l ; n= 1 0).
Two liveweight gain treatments were imposed from 21 days (one oestrous cycle) prior to insemination until D90 (end of first trimester of pregnancy). The treatments consisted of moderate (440 ± 32 g/day; n= 1 7) and low liveweight gain ( 1 22 ± 35 g/day, n= 1 6). There was no difference in pre-calving (D273) body condition score between treatments.
Measurements
From D264 to parturition (mean gestation length was 279 days, s.d. 3.5 days), a 5 ml blood sample was taken from each heifer daily in a 10 ml EDT A vaccutainer via venipuncture of the jugular vein. Samples were taken between 1 330 and 1 530 hours. Parturition occurred between two and 28 hours after the sample collected 'one day' prior to parturition. Oestrone sulphate concentration has been shown to increase rapidly in the 24 hours prior to parturition (Kindahl et al. 2002), thus there may have been substantial variation among heifers in the sample collected ' 1 day' prior to parturition,
depending on the time at which they calved. This variation was avoided by using the sample collected two days (26-52 hours) prior to parturition.
B lood samples were i mmediately placed on ice and were centrifuged at 1 500 rpm for 1 5 minutes within four hours of collection. Plasma samples were frozen at -20°e. Samples were analysed to determine oestrone sulphate concentration using double antibody radioimmunoassay (Diagnostic Systems Laboratories Australia, Gladesville, NSW). The assay sensitivity was 0.0 1 ng/ml and the inter- and intra-assay coefficients of variation were < 10%. The sample collected two days prior to parturition was analysed for all 33 heifers and samples collected 4, 6, 8 and 10 days prior to parturition were analysed for 1 7 heifers.
Parturition was classified as assisted or non-assisted and heifers and calves were weighed and sex of calf was recorded within 24 hours of parturition. Calves that were born dead or died within 1 2 hours of parturition were classified as stillborn.
Statistical methods
Data were analysed using the Statistical Analysis System (SAS version 9. 1 , SAS Institute Inc., Cary, NC, USA, 2003). Liveweight gain treatment had no effect on any of the parameters considered and was removed from the models. Maternal plasma oestrone sulphate concentration over the ten days prior to calving was analysed using the MIXED procedure considering repeated measures for each heifer. The linear model considered the fixed effects of sex of calf and the covariables gestation length, birth weight of calf and day prior to parturition. Random effects were sire of calf, and heifer to account for repeated measures. Relevant interactions were considered in all models but were not s ignificant so were excluded.
The probability of assistance at calving and the probability of stillbirth were analysed using the LOGISTIC procedure for logistic regression, with sex, sire and birth weight of calf, gestation l ength, post-partum live weight of the heifer and maternal plasma oestrone sulphate concentration two days prior to parturition considered as predictors. Non-significant effects (P>O. l ; except maternal plasma oestrone sulphate concentration two days prior to parturition) were removed from the model. Significant effects are detailed in the results. Pearson correlation coefficients were calculated using the CORR procedure.
Maternal plasma oestrone sulphate concentration
Resu lts
Six ( 1 8%) of the 33 heifers were assisted at parturition and four calves ( 1 2%, i ncluding two assisted calves) were stillborn. All heifers delivered full-term, singleton calves, of which 10 were male and 23 were female. Of the 1 7 heifers that had maternal plasma oestrone sulphate concentration records for the ten days prior to parturition, three were assisted, and one non-assisted calf was stillborn.
Assisted calves were heavier than non-assisted calves (35.8 ± 1 .5 vs. 3 1 . 1 ± 0.7 kg; P<0.05), but there was no difference in birth weight between stillborn calves and live calves (34.3 ± 2.0 vs. 3 1 .7 ± 0.8 kg). There were no differences in post-partum live weight amongst these groups, but the ratio of birth weight of calf to post-partum live weight of the heifer was greater for assisted than for non-assisted heifers (data not shown). Maternal plasma oestrone sulphate concentration two days prior to parturition was positively correlated with birth weight of the calf (r=0.4 1 ; P<0.05; Figure 1 0. 1 ) but not with post-partum liveweight of the heifer or the ratio of birth weight of the calf to post-partum live weight of the heifer. Birth weight of the calf was positively correlated with live weight of the heifer on D89 and D265 (r=0.38, P<0.05 and r=0.50, P<O.O I , respectively).
Maternal plasma oestrone sulphate concentration was relatively stable during the ten days prior to parturition, although it was greater at two days prior to parturition than at four days prior to parturition for non-assisted heifers (Figure 1 0.2). Low numbers of assisted heifers and stillborn calves limited the power of the statistical analysis. Neither the probability of a heifer requiring assistance at parturition nor the probability of calf being stillborn were affected by maternal plasma oestrone sulphate concentration two days prior to parturition.
Figure 1 0.1 . Birth weight of calves that were stillborn after a non-assisted
birth ( x ; n=2), stillborn after an assisted birth (*; n=2), born alive after an
assisted birth (+; n=4) or born alive after a non-assisted birth (0; n=25) in
relation to maternal plasma oestrone sulphate concentration two days
prior to parturition. The linear regression line represents the relationship
between maternal plasma oestrone sulphate concentration two days prior
to parturition and birth weight for all calves.
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