Sources of variation and prospects for improvement of productive efficiency in the dairy cow: a review

In this review, "productive efficiency" in dairy cows is defined as the yield of milk obtained in ratio to the nutritional costs associated with maintenance, milk synthesis and loss of body condition during lactation. Improvements in efficiency could occur as a result of changes in digestion and nutrient absorption, maintenance requirement, utilization of metabolizable energy for production or nutrient partitioning. Digestibility can be greatly enhanced by appropriate dietary manipulation. Likewise, it may be possible to reduce maintenance requirements and improve the efficiency with which metabolizable energy is used for milk synthesis by manipulation of the pattern of nutrients presented to tissues. However, these factors apparently do not respond to selection for increased milk yield, and little variation is observed among cows. In contrast, individual cows differ substantially in feed intake and in the partitioning of nutrients among body tissues. Techniques associated with genetic engineering and the early prediction of genetic merit have the potential to improve productive efficiency by manipulation of these processes. However, changes in nutrient partitioning and feed intake during lactation are coordinated by a complex network of controls that accommodate the nutrient requirements of each tissue while maintaining homeostatic balance. Future improvements in productive efficiency will therefore depend on our ability to understand the manner in which these controls operate.     

XY male pseudohermaphroditism in a captive Arabian oryx (Oryx leucoryx).

A 2-yr-old Arabian oryx (Oryx leucoryx) was presented for evaluation of abnormal genitalia and infantile behavior. The oryx had a penis and a scrotum, but testes were not palpable within the scrotum or inguinal canal. The total serum testosterone for the individual was lower than in age-matched males of the same species. Surgical exploration showed markedly hypoplastic intra-abdominal gonads, which demonstrated both testicular and uterine tissue on histologic examination. After karyotype analysis, the individual was classified as an XY male pseudohermaphrodite. This condition resembles two human intersex syndromes: embryonic testicular regression syndrome and partial gonadal dysgenesis syndrome, which occur in familial lines.     

Phosphofructokinase and Malate Dehydrogenase Participate in the In Vitro Maturation of Porcine Oocytes

Oocyte maturation depends on the metabolic activity of cumulus–oocyte complex (COC) that performs nutritive and regulatory functions during this process. In this work, the enzymes [phosphofructokinase (PFK) and malate dehydrogenase (MDH)] were tested to elucidate the metabolic profile of porcine COCs during the in vitro maturation (IVM). Enzymatic activity was expressed in U/COC and U/mg protein (specific activity) as mean ± SEM. In vitro maturation was performed with 2‐oxoglutarate (5, 10 and 20 mm ) or hydroxymalonate (30, 60 and 100 mm ) inhibitors of PFK and MDH, respectively. The PFK and MDH activities (U) remained constant during maturation. For PFK, the U were (2.48 ± 0.23) 10^?5 and (2.54 ± 0.32) 10^?5, and for MDH, the U were (4.72 ± 0.42) 10^?5 and (4.38 ± 0.25) 10^?5 for immature and in vitro matured COCs, respectively. The specific activities were significantly lower after IVM, for PFK (4.29 ± 0.48) 10^?3 and (0.94 ± 0.12) 10^?3, and for MDH (9.08 ± 0.93) 10^?3 and (1.89 ± 0.10) 10^?3 for immature and in vitro matured COCs, respectively. In vitro maturation percentages and enzymatic activity diminished with 20 mm 2‐oxoglutarate or 60 mm hydroxymalonate (p < 0.05). Viability was not affected by any concentration of the inhibitors evaluated. The U remained unchanged during IVM; however, the increase in the total protein content per COC provoked a decrease in the specific activity of both enzymes. Phosphofructokinase and MDH necessary for oocyte IVM would be already present in the immature oocyte. The presence of inhibitors of these enzymes impairs the meiotic maturation. Therefore, the participation of these enzymes in the energy metabolism of the porcine oocyte during IVM is confirmed in this study.     

Utilization of sulfur and other mineral elements by growing dairy heifers treated with bovine somatotropin

Apparent absorption and retention of Ca, P, Mg, K, Cu, Mn, Zn, and S were determined in Holstein heifers treated with recombinant bovine somatotropin (bST). Six heifers (initial BW averaged 104 kg) were assigned to various doses of bST in a 6 x 6 Latin square design with six consecutive 21-d periods. Treatments were daily i.m. injections of 0, 6.7, 33.3, 66.7, 100, or 200 micrograms of bST/kg of BW on d 8 to 21 of each period. All heifers were fed a hay-concentrate diet, and nutrient digestibilities and balances were determined on d 14 to 20 of each period. Mineral concentrations in feed, water, excreta, and blood plasma were determined with an inductively coupled argon plasma-emission spectrometer. Exogenous bST did not affect apparent absorption or retention of Ca, P, Mg, K, Cu, Mn, or Zn. Plasma CU concentration was greater (P less than .05) in heifers receiving bST (82 micrograms of Cu/dl) than in those receiving excipient (73 micrograms of Cu/dl); plasma concentrations of other elements were not affected by bST. Injection of bST did not affect S absorption, but urinary S excretion decreased (P less than .05) and S retention increased (P less than .05) as dose of bST increased. The amount of S retained (1.5 g/d) when the heifers received the largest dose of bST was approximately 50% greater than the amount retained when heifers received excipient. These results demonstrate that bST affects the postabsorptive metabolism of S. Generally, bST did not affect nutrient digestibilities. Effects of bST on dietary mineral requirements were not determined because of the relatively short (14 d) treatment periods.     

Fecal steroid analysis for evaluating ovarian function in the greater kudu (Tragelaphus strepsiceros) and lesser kudu (Tragelaphus imberbis)

Seasonal reproductive-endocrine norms have not been described for the genus Tragelaphus, which consists of seven species of African antelope. Longitudinal patterns of progesterone metabolite excretion were assessed by radioimmunoassays in fecal samples collected noninvasively (three to seven samples per week) from greater kudu (Tragelaphus strepsiceros, n = 4) and lesser kudu (Tragelaphus imberbis, n = 4). Progesterone metabolite excretion patterns revealed seasonal estrous cycles in both species, and discrimination of pregnant versus nonpregnant females was achieved in lesser kudu. These data reveal the value of fecal progesterone metabolites for establishing reproductive-endocrine norms in both zoo-maintained and free-living antelopes of the genus Tragelaphus.     

Infectivity and virulence of Australian strains of Moraxella bovis for the murine and bovine eye in relation to pilus serogroup sub-unit size and degree of piliation

The degree of piliation of 29 haemolytic and 4 non-haemolytic Australian strains of Moraxella bovis representing 7 different pilus antigen groups was determined. The infectivity and virulence for the eye was measured in steroid-treated mice and in cattle. Non-piliated strains failed to infect the murine eye. Most moderately or heavily piliated strains reproducibly produced the highest infectivity and virulence scores in mice when compared with lightly or very lightly piliated strains (p less than 0.05). Non-haemolytic, piliated strains were infective and in one instance virulent for mice. Almost similar levels of infectivity and virulence were observed for 7 representative haemolytic strains tested in both cattle and mice. The relative molecular weight of pilin sub-units was compared using sodium dodecyl-sulphate polyacrylamide gel electrophoresis. Three classes of pili, alpha, beta and gamma of ascending sub-unit size were identified among the 7 pilus antigen serogroups. Pilin sub-unit size bore no relationship to the degree of piliation but most strains that were highly virulent in mice and cattle expressed alpha and gamma sub-units. Some strains appeared capable of switching from alpha to beta or form beta to gamma sub-unit production.     

Insulin-like growth factors and binding proteins in ruminants and their nutritional regulation.

Insulin-like growth factors (IGF) are important mediators of growth, lactation, reproduction, and health. Considerable information on their role in ruminant animals has been learned in the past several years, but the precise mechanisms of their action are not known. The exact biological response of target cells is undoubtedly determined by the developmental state of the cell and synergism with other growth factors. Overall, somatomedins and their binding proteins seem to be major links between cellular developmental processes and nutrient supply. The mechanism by which nutrients control biological actions of somatomedins is not known but clearly involves the synthesis of IGF, as well as their binding proteins and receptors. In ruminants, severe feed restriction decreases circulating concentrations of IGF-I, whereas subtle alterations typical of those that occur in production systems have minimal effect. However, the responses of IGF to somatotropin are affected by modest alterations in nutritional status, including differences in nutritional status that are typically encountered in animal production systems.     

Heat Shock Protein 70 and Sex Steroid Receptors in the Follicular Structures of Induced Ovarian Cysts

The purpose of this study was to estimate the expression and relative amounts of estrogen (ER) and progesterone receptors (PR) and their isoforms as well as heat shock protein 70 (HSP70) in ovaries of rats with induced cystic ovarian disease (COD). Primary, secondary, tertiary, atretic and cystic follicles were evaluated by immunohistochemistry and total ovarian proteins were analyzed by Western blot. In the granulosa layer, growing and cystic follicles in the treated group have a higher expression of ERα than growing follicles of control individuals. In the theca interna layer, tertiary follicles presented a significantly higher expression of ERα in the treated group. An increase in total ERα protein was detected in the treated group. Granulosa cells of all growing, atretic and cystic follicles show a lower expression of ERβ in animals with COD, and the total protein expression of ERβ was lower in this group. The expression of PR was lower in the granulosa cell layer of tertiary and cystic follicles in treated animals, and theca interna layer had less intense immunostaining in this group. Although there were no differences in the expression of PR-B by Western blotting, the expression of PR-A was higher and the expression of PR-C was smaller in the treated group. An intense HSP70 immunostaining was observed in the cells of cystic follicles. By Western blotting, higher protein expression of HSP70 was detected in the ovarian samples of the control group than those of the treated ones. Ovaries of animals with COD exhibited an altered steroid receptor expression and subtype balance as compared with control animals, and an increase in HSP70 immunoexpression.     

Bovine somatotropin and lactation: from basic science to commercial application.

Bovine somatotropin (bST) results in increased milk yield and an unprecedented improvement in efficiency. Beginning in the 1930s to present day, investigations have examined animal-related factors such as nutrition, bioenergetics, metabolism, health and well being and consumer-related factors such as milk quality, manufacturing characteristics, and product safety. Overall, bST is a homeorhetic control involved in orchestrating many physiological processes. Direct effects involve adaptations in many tissues and the metabolism of all nutrient classes--carbohydrates, lipids, protein, and minerals. Mechanisms include alterations in key enzymes, intracellular signal transduction systems, and tissue response to homeostatic signals. Indirect effects involve the mammary gland and are thought to be mediated by the insulin-like growth factor (IGF) system. Specific changes include increased cellular rates of milk synthesis and enhanced maintenance of secretory cells. Indirect effects are modulated by environment and management factors, especially nutritional status. This modulation is a central component in allowing ST to play a key role in regulating nutrient utilization across a range of physiological situations. U.S. commercial use began in 1994, and adoption has been extensive. From a consumer perspective, bST was unique, and special interest groups loudly predicted dire consequences. However, introduction of bST had no impact on milk consumption, and milk labeled as recombinant bST-free occupies a minor niche market. From a producer perspective, commercial use verified scientific studies and enhanced net farm income. Overall, ST is a key homeorhetic control regulating nutrient partitioning, and the ST/IGF system plays a key role in animal performance and well being across a range of physiological situations.