Two herds with high (HS) or low (LS) susceptibility to pasture bloat have been selected divergently at Ruakura since 1972 using field bloat scores. The present paper continues studies on weights of rumen digesta, in 92 HS and 81 LS cull cattle experimentally slaughtered from 1985 to 1990. Traits recorded included pre-slaughter weight (PSW), hot carcass weight (HCW), the fresh weight, dry matter percentage (DM%) and dry weight of rumen digesta, weight of full abomasum and omasum, carcass composition, and weights of heart, liver, kidney and omental fat. In addition, pre-feeding and post-feeding girths at the last rib were obtained on 61 2- to 8-year old cows in mid-lactation, as a possible predictor of variation in rumen contents and in bloat susceptibility. The LS herd had a 10% greater PSW than the HS herd (P<0.001), and adjustments for body size were therefore made below to all traits from the abattoir except HCW and DM%. The fresh weights of digesta were similar in the two herds, but the DM% of digesta was 17% greater in LS than HS cattle (P<0.001). The weight of abomasum and omasum was 15% greater in LS than HS cattle (P<0.001), but there was no significant herd effect on fasting weight loss. Heart and kidney weights were 8 to 9% greater in LS than HS cattle. Ratios of rib girth to chest girth, in the absence of bloat, were not significantly different between herds at 1.172
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 67-72, 1991
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