Dystocia in 2-year-old beef heifers is a major factor limiting the willingness of farmers to breed 15-month-old heifers in New Zealand. Foetal oversize relative to the size of the heifer is a contributor to dystocia. This study aimed to determine the effect on foetal weight of maternal liveweight change during joining and early pregnancy. Sixteen 15-month-old Angus heifers were allocated to moderate (444 ± 30 g/day) or low (109 ± 28 g/day) liveweight-gain treatments for 21 days prior to and 91 days after insemination. Gravid uteri were recovered on day 91 of pregnancy. Foetuses from the low-fed heifers tended to be heavier than foetuses from the moderate-fed heifers (215.6 ± 6.7 g and 198.4 ± 6.8 g, respectively; P=0.09). Foetal weight per 100 kg maternal weight was greater (P<0.01) in foetuses from the low treatment (58.9 ± 2.5 g/100 kg) than in foetuses from the moderate treatment (47.4 ± 2.6 g/100 kg). Weight of foetal membranes was greater (P<0.05) in the low treatment (262 ± 16 g) than the moderate treatment (213 ± 16 g). Foetal weight was correlated with cotyledon weight (r=0.59; P<0.05). Moderate compared with low maternal liveweight gain reduced foetal weight relative to maternal live weight.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 117-120, 2007
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