Dairy production in pakistan

Effects of Nutrition on Reproduction in Dairy Cattle

Nutritional status and nutritional management are essential components of overall herd management. The Primary conditions of malnutrition affecting reproduction include clinical deficiency and excessive intake of a particular nutrient. Secondary conditions comprise those in which other constraints result in a nutritional imbalance. Therefore, a suboptimal plane of nutrition can result in impaired reproductive performance. This observation holds true for both the developing replacement dairy heifer and the lactating dairy cow. This chapter reviews the effects of nutrition on the reproductive biology of the dairy cow, concerning both onsets of puberty and lactation
Puberty:
Plane of nutrition also can influence the onset of puberty. Plane of nutrition can inhibit the onset of puberty in heifers at adequate body weight, size, and age. Gonzalez-Padilla and associates22 demonstrated that 14-month-old heifers could be maintained in a prepubertal state and then suddenly made to ovulate by increasing nutrient intake. It generally is accepted that the physiologic cause of the delay is the result of inhibition in the pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus and the subsequent release of luteinizing hormone (LH) from the pituitary gland. It also has been demonstrated that GnRH secretion is extremely sensitive to the nutritional status of the animal. Furthermore, insulin may play a role in energy-yielding nutrients, as it binds receptors in the region of the brain thought to regulate GnRH secretion.23 Conditions such as disease and parasitism can influence nutritional status by altering the intake or absorption of nutrients. Bumgarner and coworkers24 reported that calves treated with anthelmintics in both mid-June and mid-July had a reduction in fecal oocyte counts and increased daily gain. Numerous other studies demonstrated improved weight gains from the use of anthelmintics.25 Respiratory disease that results in severe lung damage can also result in poor performance of growing dairy heifers. Sudden onset of disease can result in a transient period of anestrus.
Lactating cow:
The nutritional balance of a dairy cow during the periparturient period can have a tremendous influence on fertility and reproductive efficiency. During the final 30 days of gestation, lactation is initiated, with the production of colostrum and final growth of the fetus. At day 270 of gestation, the uterus and fetus require greater than 1600kcal per day.26 Concurrent with increased nutrient

requirements, the prenatal cow experiences a marked decrease in dry matter intake. Severe anorexia or an imbalance of nutrient intake can predispose the animal to several metabolic diseases that constitute the parturition disease complex.27 These diseases are not independent but can increase the risk of subsequent problems. For example, Curtis and coworkers28 reported that cows with hypocalcemia were at increased risk of suffering dystocia, retained fetal membranes, and ketosis. Dystocia and retained fetal membranes are predisposing factors for postparturient uterine disease. Markusfeld27 documented that cows experiencing postparturient uterine disease had a decreased milk yield for the lactation and increased number of days open. Retained fetal membranes also have been influenced by selenium and vitamin E supplementation. Cows that experienced retained fetal membranes may have had a lower plane of nutrition. Disrupted intake accompanied by disrupted energy metabolism can result in an increased level of circulating ketone bodies. Miettinen29 reported that cows with higher concentrations of circulating ketone bodies had more days to first service, decreased first service conception rates, and more days open. More recently, cows with serum beta-hydroxybutyrate concentrations of 1100μmol/L in weeks 1 and 2 of lactation were found to have increased risk of conception failure.30 These studies make a significant statement regarding the importance of periparturient health and metabolism on fertility and reproductive efficiency during the subsequent lactation. The primary modulator of reproductive function appears to be energy intake and the energy status of the animal.
Energy:

Energy or energy balance is considered the primary nutrient relative to the nutritional modulation of the reproductive function of the dairy cow. The energy balance of the animal is most simply expressed by the equation
Energy balance = energy intake (milk energy secreted maintenance energy)
With the initiation of lactation, the acceleration produced exceeds the increase in Lactating cows consumes inadequate dietary energy peak milk production. As a result, early-lactation cows experience negative energy. Based on energy calculations, cows in early lactation can experience as much as a 20-Mcal deficit of net energy. Cows compensate during this delay in energy intake by mobilizing stored body energy. For the early postpartum cow, this energy is generated primarily from stored adipose tissue. One kilogram of body fat contains 6Mcal of stored energy.31 Therefore, early-postpartum dairy cows must rely on oxidation of body fat for energy to compensate for inadequate energy intake. The nutritional challenge of negative energy balance is significant and can adversely affect reproductive performance.

MINERALS AND VITAMINS

Several excellent reviews on the effects of mineral nutrition and status on the reproductive function of dairy cattle are available.64–68 These surveys discuss the impact of mineral and vitamin status on reproductive function and performance. Calcium as an individual nutrient has been associated with poor reproduction when severely deficient. Calcium, the relationship of calcium to phosphorus, and the balance of calcium with vitamin D also have been linked to altered reproductive performance. Ward and coworkers69 reported that cows fed high-calcium and high–vitamin D diets antepartum had more rapid uterine involution, fewer days to first service, and fewer days open. Hignett and Hignett70 often are cited for their work with the calcium-phosphorus balance and vitamin D to support normal reproduction. From their results, a minimum calcium-to-phosphorus ratio of 1.5:1 and a minimum daily P intake of 30g were suggested. , current NRC recommendations agree to
data, but data relating recommended levels to fertility and reproductive performance have not been reported. Macromineral and vitamin nutrition also can indirectly affect reproductive health and performance. Curtis and associates28 described the relationships between hypocalcemia and periparturient disorders. Parturient hypocalcemia significantly increased the odds ratio for dystocia and retained placenta. These investigators concluded that the loss of muscle tone associated with hypocalcemia could reduce normal uterine function. Early research found that feeding low-calcium diets prevented parturient paresis.71 Practical dry cow diets often are low in calcium, but cattle suffer from hypocalcemia. Block72 reported the advantage of shifting the dietary cation-anion balance on calcium status. Manipulation of the anionic content of the diet has been used to lower the incidence of hypocalcemia and clinical milk fever. As discussed earlier, decreasing these metabolic disorders probably would improve reproduction. Morrow73 reported that dairy heifers suffering from phosphorus deficiency had high rates of infertility as measured by services per conception. Increasing phosphorus in the diet returned blood levels to normal, with improved fertility.