Three breeds (20 Friesian, 20 Jersey and 20 Jersey/Friesian crossbred multiparous cows) were used to determine the effect of breed on indicators of metabolic status and the post partum anovulatory interval (PPAI). Effect of breed on circulating concentrations of metabolites and hormones, liver mRNA levels and PPAI was established. Weekly blood samples were taken for the first 6 weeks of lactation. Liver biopsy samples were taken from a sub-sample of cows of each breed between 23-33 days post partum, to determine levels of expression of T-GHR, GHR-1A and IGF-1 receptors using RT-PCR. Milk progesterone analysis was used to determine PPAI. There was a significant breed effect on circulating concentrations of â-hydroxy butyrate (P<0.01), non-esterfied fatty acids (P<0.001), triacylglycerols (P<0.001) and leptin (P<0.01), with Jersey cows having higher concentrations of these hormones and metabolites than Friesian or crossbred cows. Despite the concentration differences between breeds, only leptin showed a significant difference (P<0.01) in the rate of change in concentration across time between the breeds. Jersey cows were observed to have shorter PPAI (34 vs 42 and 44 days for Friesian and crossbred cows respectively: SED 6 days) but this was not statistically significant (P=0.18). There was no difference in the expression of mRNA levels of TGHR, GHR-1A and IGF-1 receptors in the liver. It appears that grazing Jersey cows have a different fat metabolism, which affects the regulation of circulating leptin concentrations and this may have contributed to their apparent ability to return to cyclicity earlier.
Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 390-396, 2006
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