Influences of nutrition and metabo lism on fertility of dairy cows

During early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrien t balance. Homeorrhetic controls assure that nutrients are partitioned to favor lactation at the same time that homeostasis secures survival. However, unrestrained metabolic disturbances often lead to diseases which, in turn, dramatically decrease both productive and reproductive performance. Negative nutrient balance ha s been associated with compromised immune and reproductive functions in dairy cows. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids and ketone bodies postpartum have disruptive and detrimental effects on the oocyte, granulosa and immune cells. Negative nutrient balance is associated with changes in the pattern of ovarian follicle growth which can indirectly affect oocyte quality. Some of this disruption seems to be the result of endocrine and biochemical changes that alter the micro- environment of the growing and maturing oocyte. In addition, cows under negative nutrient balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period. The underlying mechanism for resumption of ovulatory cycles seems to be associated with metabolic signals and regulatory hormones primarily insulin and insulin- like growth factor (IGF)-1, which link nutritional status with gonadotropin secretion, recoupling of the growth hormone-IGF system, and follicle maturation and ovulation. Feeding diets th at promote increases in plasma glucose and insulin may improve the metabolic and endocrine status of cows in early lactation. Furthermore, fertility in postpartum cows is also determined by uterine health. Reductions in circulating concentrations of Ca and antioxidant vitamins around parturition are also linked with impaired immune competence and result in greater risk of uterine diseases that impair reproduction. Specific nutrients and dietary ingredients have been implicated to affect reproduction in cattle. Excess intake of dietary protein has been suggested as detrimental to fertility, although feeding excess of dietary protein can no longer be justified. Addition of moderate amounts of supplemental fat to the diet improves caloric intake, modulates prostaglandin F2  secretion by the uterus, affects ovarian dynamics, enhances luteal function and embryo quality, and has moderate positive effects on fertility. More specifically, some fatty acids might impact fertilization rate and embryo quality in dairy cows. On the contrary, some dietary ingredients, such as gossypol, when ingested in large quantities decrease fertility of dairy cows because of its negative effects on embryo quality and pregnancy maintenance.(AU)

Influences of nutrition and metabo lism on fertility of dairy cows

During early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrien t balance. Homeorrhetic controls assure that nutrients are partitioned to favor lactation at the same time that homeostasis secures survival. However, unrestrained metabolic disturbances often lead to diseases which, in turn, dramatically decrease both productive and reproductive performance. Negative nutrient balance ha s been associated with compromised immune and reproductive functions in dairy cows. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids and ketone bodies postpartum have disruptive and detrimental effects on the oocyte, granulosa and immune cells. Negative nutrient balance is associated with changes in the pattern of ovarian follicle growth which can indirectly affect oocyte quality. Some of this disruption seems to be the result of endocrine and biochemical changes that alter the micro- environment of the growing and maturing oocyte. In addition, cows under negative nutrient balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period. The underlying mechanism for resumption of ovulatory cycles seems to be associated with metabolic signals and regulatory hormones primarily insulin and insulin- like growth factor (IGF)-1, which link nutritional status with gonadotropin secretion, recoupling of the growth hormone-IGF system, and follicle maturation and ovulation. Feeding diets th at promote increases in plasma glucose and insulin may improve the metabolic and endocrine status of cows in early lactation. Furthermore, fertility in postpartum cows is also determined by uterine health. Reductions in circulating concentrations of Ca and antioxidant vitamins around parturition are also linked with impaired immune competence and result in greater risk of uterine diseases that impair reproduction. Specific nutrients and dietary ingredients have been implicated to affect reproduction in cattle. Excess intake of dietary protein has been suggested as detrimental to fertility, although feeding excess of dietary protein can no longer be justified. Addition of moderate amounts of supplemental fat to the diet improves caloric intake, modulates prostaglandin F2  secretion by the uterus, affects ovarian dynamics, enhances luteal function and embryo quality, and has moderate positive effects on fertility. More specifically, some fatty acids might impact fertilization rate and embryo quality in dairy cows. On the contrary, some dietary ingredients, such as gossypol, when ingested in large quantities decrease fertility of dairy cows because of its negative effects on embryo quality and pregnancy maintenance.

Performance of lactating dairy cows managed on pasture-based or in freestall barn-feeding systems.

The objective was to compare productive and metabolic responses of lactating dairy cows managed on 2 pasture-based systems using a concentrate supplement (n = 16) with those of a freestall housing system (n = 24). In a 259-d experiment, 3 multiparous Holstein cows were assigned at calving to each of 4 replicates of 2 pasture systems. For system 1, winter pastures were a mixture of rye, ryegrass, and crimson and red clover; summer pastures were pearl millet. Pasture system 2 included a rye-ryegrass mixture during winter and bermudagrass during summer. Pregraze herbage mass averaged 2.3 and 3.6 Mg/ha for winter and summer pastures, respectively; however, during August through September, pearl millet pregraze mass was reduced to about 1 Mg/ha. Daily dry matter intake by cows on pasture averaged 24.7 kg/d in winter and 19.0 kg/d in summer, of which 55% was from pasture; that of cows in confined-housing averaged 23.6 kg/d. Cows in confinement produced 19% more milk (29.8 vs. 25.1 kg/d) than those on pasture systems. Differences in concentration of milk fat, protein, or urea N were not detected among treatment groups. Grazing cows lost more body weight than confined cows (113 vs. 58 kg) and had lower concentrations of plasma glucose in the early weeks postpartum. Despite greater milk yield by cows housed in freestalls, milk income minus feed costs including that of pasture was similar for the 3 management systems. Although these pasture systems might be a viable management system in the southeastern US, extensive loss of body weight immediately postpartum for pasture-based cows are a potential concern.

Protein degradability and calcium salts of long-chain fatty acids in the diets of lactating dairy cows: productive responses.

Our objective was to evaluate the effect of excessive intake of ruminally degradable crude protein [11.1 and 15.7% of dietary dry matter (DM)] and supplemental fat (Ca salts of long-chain fatty acids at 0 or 2.2% of dietary DM) on the productive performance of lactating Holstein cows (n = 45) during the first 120 d postpartum. The main N sources were soybean meal and urea in the diets with high concentrations of degradable protein versus a combination of vegetable and animal by-product feedstuffs in the diets with less degradable protein. Cows fed the diets with excess degradable protein had slower rates of increase in DM intake (DMI) and milk production, had lower plasma insulin and greater plasma glucose and urea concentrations, and lost more than twice the body weight of cows fed the diets with less degradable protein. Supplemental fat in the highly degradable protein diet reduced the loss of body condition, stimulated DMI, and reduced concentrations of plasma nonesterified fatty acids early postpartum compared with the highly degradable protein diet without added fat. Without affecting DMI, supplemental fat stimulated milk production (2 kg/d) starting at 3 wk postpartum. During early lactation, DMI and milk production were sensitive to the degree of ruminal degradability of protein and energy supplementation in the form of fat.

Protein degradability and calcium salts of long-chain fatty acids in the diets of lactating dairy cows: reproductive responses.

Multiparous Holstein cows (n = 45) were assigned at calving to one of four diets arranged in a 2 x 2 factorial design. The two main factors were dietary concentration (dry matter basis) of 1) degradable intake protein (11.1 or 15.7%) and 2) supplemental fat (Ca salts of long-chain fatty acids; 0 or 2.2%). Soybean meal and urea were replaced with less degradable protein meals (corn gluten meal, meat and bone meal, fish meal, and blood meal). During the first 9 wk postpartum, cows fed diets containing the greater concentration of highly degradable protein demonstrated less follicular development on their ovaries, were delayed in their first luteal activity postpartum (25.2 vs. 38.6 d), accumulated less luteal tissue (< 15 vs. > 70 mm), and had lower plasma progesterone accumulated over time. The supplementation of Ca salts of long-chain fatty acids to the 15.7% degradable protein diet doubled the number of corpora lutea, reduced time to first rise in progesterone by 6 d, doubled the number of normal luteal phases, and restored the pattern of accumulated plasma progesterone concentrations to a pattern that was similar to that induced by other diets. Cows were synchronized to estrus and inseminated at approximately 65 d postpartum. Pregnancy rate was increased from 52.3 to 86.4% when fat was supplemented. Cows fed fat tended to have more corpora lutea and a larger corpus luteum and accumulated more plasma progesterone than did cows not fed fat. Diets containing excess degradable protein or Ca salts of long-chain fatty acids influenced ovarian structures and reproductive performance.