Dairy Pipeline: October 1999
Ray L. Nebel
Extension Dairy Scientist, Reproductive Management
Female fertility refers to any factors directly related to the heifer/cow that may alter her probability of becoming pregnant, including uterine condition, nutritional status, recent changes in body condition status, and health. Many have shown that fertility increases as interval from calving to first service increases up to 70 days postpartum. Repetitive estrous cycles are necessary to confer fecundity. Conception rate and estrus expression improves with each sequential estrous cycle from first ovulation to the third estrous cycle. For maximum fertility cows should be on the third or higher estrous cycle when AI commences. Hopefully, first ovulation will transpire 17 to 30 days postpartum so that the third ovulation will occur by day 50 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 of uterine environment recovery.
Calving places the cow at risk for metritis, retained placenta, dystocia, milk fever and other metabolic diseases that contribute to a decline in the fertility. 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 magnitude of metritis or abnormal lochia in reducing conception rate; 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 a secondary disease, such as metritis or ketosis. Lameness has had varying effects on fertility and may depend on the time postpartum in which it occurs and the severity of the problem. Metritis, abnormal lochia, 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 intake that will reduce fertility. Excessive energy or protein in the dry cow diet can create metabolic problems as readily as low energy or low protein diets. Excessive tissue mobilization associated with low dry matter intake in the late dry period is a risk factor for significant parturient problems. In addition mineral supplementation, particularly Ca, Mg, and Se are important in the control of milk fever, grass tetany, and retained placenta. 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 .5 to .75 units of body condition in the first four weeks of lactation, more extreme condition loss will predispose them to lower conception rates at first service.