Management of dry and transition cows to improve energy balance and reproduction.

Fertility of dairy cows has decreased for the past several decades. Measures of energy balance (EB; e.g., change in EB, EB nadir, cumulative negative EB, or duration of negative EB) are related to reproductive performance. Our research group has concluded that modification of diets fed during the dry or transition period are unlikely to have significant effects on postpartum EB and fertility. Rather, more radical alterations in dairy management are needed if energy status of postpartum cows is to be improved. We have examined the potential to alter EB by shortening or eliminating the dry period. In an initial study, the effects of a 56, 28, and 0 d dry period on ovarian dynamics and reproductive performance of dairy cows were examined. Postpartum EB was improved by reducing the dry period; however, only significantly for the 0 d dry period. Cows on the 0 d dry period did not experience negative EB. Improvements in EB were a reflection of lower milk production and greater feed intake. Consistent with the improvements in EB, time to first ovulation and first service, first service conception rate, services per conception, and days open were all improved by reduction of dry period length. Because small animal numbers were used in the study, a second study was conducted on a commercial dairy with many more animals to determine if results from the initial trial could be duplicated. A comparison was made between a 55 and 34 d dry period. Shortening the dry period resulted in fewer days to first ovulation, fewer days open, and a greater percentage of cows pregnant at 150 days in milk, although the improvements in the latter two variables were only significant for cows in their third or greater lactation. A current study is being performed in a large commercial dairy to examine the effects of eliminating the dry period on reproduction utilizing a large commercial dairy.

Nutritional and management strategies for the prevention of fatty liver in dairy cattle.

Fatty liver occurs in dairy cattle during periods of elevated blood non-esterified fatty acids (NEFAs). Elevated blood NEFAs are associated with hormonal changes at parturition and negative energy balance. Approaches for preventing fatty liver include inhibition of fatty acid mobilization from adipose tissues and altering hepatic metabolism to enhance fatty acid oxidation or export as a constituent of very low-density lipoproteins (VLDL). Nutritional and management strategies to implement these approaches have been examined. Increasing energy density of diet, either by increasing non-fiber carbohydrate or fat, has failed to prevent fatty liver. Two nutritional supplements, ruminally-protected choline and propylene glycol, have proven effective at preventing fatty liver. Choline probably enhances hepatic VLDL secretion. Propylene glycol most likely reduces fatty acid mobilization from adipose tissue. Shortening or eliminating the dry period is a management strategy that reduces the magnitude of negative energy balance after calving and triglyceride accumulation in the liver.

Effects of intravenous triacylglycerol emulsions on lymphocyte responses to mitogens in fasted dairy cows undergoing intense lipomobilization.

The objective of the study was to assess the effects of intravenous infusion of triacylglycerol (TAG) emulsions derived from different lipid sources on responses to mitogens of peripheral blood mononuclear cells (PBMC) isolated from fasted dairy cows. Six multiparous, non-pregnant, non-lactating Holstein cows were used in a replicated 3x3 Latin Square design. For 4 d, cows were fasted and infused intravenously with a 20% TAG emulsions derived from tallow (TA), linseed oil (LO) or fish oil (FO). Fasting was employed to induce energy deficit and lipid mobilization. Emulsions were administered for 20 to 30 min every 4 h throughout the 4 d fast at a rate of 0.54 g TAG/kg BW/d. Blood samples were taken before the first infusion, and then every 24 h during the fast. Blood was utilized to assess DNA synthesis, IgM and interferon-gamma (IFN-gamma) secretion by PBMC stimulated with mitogens. In TA infused cows there was a decline of PBMC ability to respond to mitogens, which was significant 48 h after initiation of the infusion period for DNA synthesis and IFN-gamma secretion. In LO or FO infused cows, PBMC responses to mitogens were not altered during the infusion period, and in some cases PBMC responses to mitogen was improved at 72 and 96 h after initiation of treatments. Effects of TAG infusion on PBMC responses to mitogens depended on the lipid source suggesting that LO or FO can attenuate the negative effects of fasting on immune functions.

Dry matter intake and energy balance in the transition period.

It is easy, based on theoretic considerations, to make the argument that maximizing DMI is important to minimize postpartum complications and losses in milk production that may be associated with them. However, research over the past several years provides ample evidence that successful "passage" through the periparturient period is more complicated than simply maximizing feed intake. Anecdotal evidence from veterinarians and nutrition consultants also confirm that feeding low-NDF diets to achieve high prepartum feed intakes during the prefresh transition period does not necessarily solve fresh-cow problems. Perhaps more important than maximizing feed intake is to minimize the likelihood of cows experiencing large drops in feed intake immediately before parturition. Retrospective analysis of existing data sets indicates that this hypothesis has merit; research must be conducted to vigorously test it. Until then, it seems reasonable to try to achieve high DMI, if it can be sustained through parturition. If it cannot, perhaps a more conservative approach is to limit voluntary intake by increasing dietary fiber, because data suggests that cows fed in such a manner experience less dramatic decreases in feed intake as parturition approaches. We examined the importance of parity, body condition score, and various diet components that may influence DMI during the final 3 weeks before parturition, but they only explained 18% of the variation in intake among cows. Clearly, there are many other factors that affect intake that need to be identified. Aspects of farm management that may influence animal stress need to be investigated, particularly during the prefresh transition period when cows are inherently prone to reductions in feed intake.