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Previous studies have shown that 35 — 40 % ofmodern dairy cows experience ovarian disturbances during early lactation. Even though negative energy balance (NEB) has been implicated as a regulator of ovarian function, the exact metabolite(s) or hormone(s), which mediate this effect is still not clear. In this study, we investigated the relationship between blood metabolites (NEFA, BHB and glucose) and plasma insulin like growth factor-I (IGF-I) and ovarian dysfunction. Thirty three Holstein-Friesian cows were fed a lactational ration ad libtium and were inseminated at observed oestrus starting from 56 days post calving. Three times weekly milk samples and weekly blood samples were collected from cows from calving until confirmed pregnant. Cows were placed into “NORMAL” or “ABNORMAL” categories of ovarian activity based on their milk progesterone profiles. The days to first service were 71 ± 2 in “NORMAL” and 78 ± 6 in “ABNORMAL” animals. The calving to conception interval (days open) was shorter in the “NORMAL “ than the “ABNORMAL” group (90 ± 8.7 vs 119 ± 15.2 days). IGF-I levels were significantly lower in the “ABNORMAL” group from 2 until 7 weeks after calving (P<0.02) and NEFA concentrations were higher in the “ABNORMAL” cows in the early postpartum period (P<0.03). There was no significant difference in either plasma BHB or glucose. This study confirms that elevated plasma NEFA concentrations are associated with “ABNORMAL” ovarian activity. The most significant difference was in plasma IGF-I concentrations, which stayed lower for nearly 2 months in the “ABNORMAL” animals.
Achieving adequate fertility is essential in any dairy unit, but is compromised by genetic selection for increased yield. Selection has altered the somatotrophic axis and resulted in cows which mobilise more body tissue for milk production in early lactation, thus prolonging both the depth and duration of the post partum negative energy balance. Poor energy status is reflected in altered metabolic parameters including raised urea and decreased insulin-like growth factor-I (IGF-I) and insulin concentrations, which adversely affect ovarian cyclicity and early embryo survival. Attempts to optimise the diet in terms of energy and protein content have generally been aimed at increasing milk production further rather than improving fertility. Advances in biosensor technology now provide us with the opportunity to monitor production, fertility and health parameters of each cow. Integration of this information should improve the timing for inseminations and could assist in selecting diets more suited to the needs of the individual cow. Genetic selection may in future be used to produce cows optimised for a particular type of management system. In both cases we need a greater understanding of the rules governing nutrient partitioning at different stages of the cows' life cycle to ensure that diets selected are cost effective and achieve an appropriate balance in promoting production, reproduction and health.
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