Angus selection and control herds in two long-term breeding studies were compared for muscle glycogen and blood parameters pre-slaughter. Trial 1 involved 3 years of bulls (n=85) from a yearling-weight (W) selection herd and a control (C1) herd, differing by 19% in yearling weight. Trial 2 involved one year of steers (n=45) from an experiment to increase age at puberty (A+ herd) or to reduce age at puberty (A- herd), relative to a control (C2) herd, with age at puberty differing from the C2 mean by 11% (A+) and -10% (A-). In Trial 1, muscle biopsies were taken for glycogen assay (Years 1 and 2), and blood samples were taken (Years 1-3) for creatine kinase, cortisol, lactate, non-esterified fatty acids (NEFA) and glucose; animals in Trial 2 (Year 2 only) were sampled at the same time as Trial 1. Samples were taken at 17 months of age (Year 1), 10 and 19 months (Year 2), and 19 and 20 months (Year 3, with an extra blood trait added). Muscle glycogen concentration was 19% higher in the W than C1 herd (P<0.05), and it was significantly lower in the A+ herd than in the other two herds (P<0.001). Cortisol (P<0.05) and glucose concentrations (P<0.01) were lower in the W than the C1 herd; NEFA was higher in the C2 herd than in the A- or A+ herds (P<0.05). No other blood parameters differed between herds. Repeatabilities for the 5 main blood traits in Trial 1 ranged from 0.14 to 0.38, being highest for creatine kinase (if excluding outliers), but repeatabilities were all low in Trial 2 (highest value only 0.13). The main conclusions came from Trial 1, in which most data had been collected, namely that across-year differences were found for 3 traits between herds (muscle glycogen, cortisol and glucose).

CA, Morris, MG Lambert, TW Knight, and AD Fisher

Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 132-134, 2000
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