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Virginia Cooperative Extension - Knowledge for the CommonWealth

Transition period and reproductive performance

Dairy Pipeline: July 2002

Ray L. Nebel
Extension Dairy Scientist,
Reproductive Management
(540) 231-4432

One of the major factors influencing fertility in dairy herds is calving. Early calving places the cow at risk for metritis, retained placenta, dystocia, milk fever and other metabolic diseases that contribute to the decline in fertility of the population. Typically cows that experience a postpartum problem will have conception rates one half that of normal cows. Ketosis and lameness do not appear to have the same effect as metritis in reducing conception rates; however, many studies have identified these conditions as having a significant impact on fertility. The impact of retained placenta on conception rate may be dependent upon the development of secondary disease, such as metritis or ketosis. Lameness has had varying impacts on fertility and may depend on the time postpartum when it occurs and the severity of the problem. Metritis and systemic metritis may be perceived as conditions associated with hygiene and stress at calving. Retained placenta, milk fever, uterine prolapse, and grass tetany are directly associated with dry cow feeding and mineral content in dry cow rations. Ketosis, laminitis, fatty liver, and ovulatory dysfunction, particularly anestrus, may be viewed as metabolic dysfunctions associated with energy balance. In addition, excessive body condition loss should be detected as a problem with energy management and will reduce fertility. The magnitude and duration of negative energy balance depends more on dry matter intake than milk yield. Prevention of excessive mobilization of body fat in the first 4 weeks of lactation is of primary importance for subsequent fertility. Cows will tolerate a loss of approximately 1 body condition scoring unit in the first 4 weeks after calving; more extreme condition loss will predispose her to lower conception rates at first service. Researchers at the University of Florida have shown that the pregnancy rates to timed AI was approximately 12% lower for cows with a body condition score less than 2.5, compared to cows with a body condition score greater than 2.5. The mobilization of body fat post-calving actually begins prior to parturition, as seen from profiles of serum lipids. One unit change in body condition score represents about 120 lbs of body weight change and about 400 Mcal of energy. The summer is the most challenging period to have cows transition from the dry lot to the milking herd. Keeping cows as cool and comfortable as possible is a major key in having the herd transition into the breeding herd successfully. Feeding management that maximizes dry matter intake is also essential to minimize body condition loss and have ovarian cycles start back approximately 3 weeks after calving. Ideally, the third ovulation will occur by 50 days postpartum when uterine involution and repair will also be complete. Increased negative energy balance may delay first ovulation 60 to 75 days or longer extending the postpartum effects and recovery of the uterine environment.

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