Prolonged postpartum anoestrous intervals (PPAI) are the major source of infertility in New Zealand dairy cows. Postpartum supplementation with mono propylene glycol (MPG) was previously shown to reduce PPAI in heifers. The present experiment tested this treatment in four large commercial dairy herds. During the six-week period preceding the planned start of mating (PSM; week 0), cows were drenched either once (1xMPG) or twice (2xMPG) daily with 200 ml MPG, or served as untreated controls (CON). Analyses were confined to the group of cows that were anoestrus at Week –6 or calved between Week –6 and Week –4 relative to PSM (n = 662 to 669 per treatment). Change in body condition score between Week –6 and Week –1(∆BCS), and proportion of cows that were anoestrus at Week –1 were influenced by herd, age and time of calving (P<0.05) but not by treatment (P>0.1). Treatment did not influence the proportion of anoestrous-treated cows inseminated after oestrus detection (n =263), or the pregnancy rate among all cows. Pre-mating supplementation with MPG did not influence ∆BCS, the percentage of cows that were anoestrus at Week –1, or rates of submission and conception. Change in BCS affected both milk yield and pregnancy rates, where cows that gained BCS produced less milk but showed higher 6-week pregnancy rates. This study highlighted that key factors influencing the percentage of anoestrus at PSM are cow age, time of calving and management of the herd.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 53-57, 2004
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