Paradoxical increases of circulating nonesterified fatty acids in somatotropin treated cattle undergoing mild disturbances

Metabolic Responses to Epinephrine by Periparturient Dairy Cows Fed Prepartum Diets Differing in Predicted Metabolizable Protein Supply

We determined the effects of prepartum dietary metabolizable protein (MP) supply on lipolytic and glucose response to epinephrine stimulus during the periparturient period. Twelve non-lactating cows in second or greater pregnancies were assigned to a low MP (LMP) diet formulated to provide ~900 g/day MP or a high MP (HMP) diet to provide ~1,100 g/day MP. Cows received prepartum diets from 28 days before expected parturition to day of parturition and then received a common lactation diet until 35 days postpartum. Blood was sampled weekly to day −7, daily to day 7, and weekly through day 35 relative to parturition for analysis of glucose, non-esterified fatty acids (NEFAs), 3-hydroxybutyrate (BHB), urea N, and total protein concentrations. Epinephrine challenges were conducted on day −10 before expected parturition and days 7 and 14 postpartum. Epinephrine [1.4 μg/kg body weight (BW)] was administered via jugular vein and blood was collected from the opposite jugular vein from −45 min to +120 min relative to epinephrine administration. Plasma was analyzed for glucose and NEFA concentrations. Prepartum dry matter intake (DMI) (14.7 and 12.6 ± 1.5 kg/day for LMP and HMP, respectively), postpartum DMI (21.4 and 19.4 ± 1.3 kg/day for LMP and HMP, respectively), and 4% fat-corrected milk (FCM) (37.0 and 36.8 ± 1.5 kg/day for LMP and HMP, respectively) did not differ significantly between diets. Cows fed HMP had higher plasma concentrations of urea N prepartum than cows fed LMP (14.0 vs. 7.9 ± 0.8 mg/dl). Cows fed HMP tended to have greater prepartum concentrations of total protein in plasma than those fed LMP (7.5 vs. 7.0 ± 0.2 g/dl). The area under the curve (AUC) for NEFA response to epinephrine did not differ between diets, but differed by day relative to parturition [8,284, 29,018, and 18,219 ± 2,302 min × (μeq/l) for days −10, 7, and 14, respectively]. Maximal response of NEFA concentration to epinephrine was greater for HMP than for LMP (744 vs. 438 ± 72 μeq/l). The glucose AUC did not differ between diets or among days. Lipolytic response, but not glucose response, to epinephrine was enhanced during the early postpartum period relative to the late dry period. However, those responses were not affected by prepartum MP supply.

Adrenergic Tone as an Intermediary in the Temperament Syndrome Associated With Flight Speed in Beef Cattle

The temperament of farm animals can influence their resilience to everyday variations within the managed production environment and has been under strong direct and indirect selection during the course of domestication. A prominent objective measure used for assessing temperament in beef cattle is the behavioral flight response to release from confinement in a crush or chute. This behavioral measure, termed flight speed (also known as escape velocity) is associated with physiological processes including body temperature, feeding behavior, growth rate, carcass composition, immune function, and health outcomes. This review examines the functional links between this suite of traits and adrenergic activity of the sympathetic nervous system and the adrenomedullary hormonal system. It is suggested that flight speed is the behavioral aspect of an underlying “flightiness” temperament syndrome, and that elevated adrenergic tone in animals with a high level of flightiness (i.e., flighty animals) tunes physiological activities toward a sustained “fight or flight” defense profile that reduces productivity and the capacity to flourish within the production environment. Nonetheless, despite a common influence of adrenergic tone on this suite of traits, variation in each trait is also influenced by other regulatory pathways and by the capacity of tissues to respond to a range of modulators in addition to adrenergic stimuli. It is suggested that tuning by adrenergic tone is an example of homeorhetic regulation that can help account for the persistent expression of behavioral and somatic traits associated with the flight speed temperament syndrome across the life of the animal. At a population level, temperament may modulate ecological fit within and across generations in the face of environmental variability and change. Associations of flight speed with the psychological affective state of the animal, and implications for welfare are also considered. The review will help advance understanding of the developmental biology and physiological regulation of temperament syndromes.

Effect of bovine genotype on innate immune response of heifers to repeated lipopolysaccharide (LPS) administration

This pilot study provides a preliminary assessment of the impact of genotype on acute innate immune pro-inflammatory, metabolic and endocrine responses to repeated lipopolysaccharide (LPS) administered to growing heifers. Heifers (n = 4/genotype) were from unselected (stable milk yield since 1964, UH) or contemporary (CH) Holstein cows that differed in milk yield (6200 vs 11,100 kg milk/305 d) or from contemporary Black Angus (CA) cows bred to contemporary Red Angus bulls. Heifers were challenged with iv administration of 0.5 μg LPS/kg body weight on day 1 (Challenge 1) and d 5 (Challenge 2) of study to assess endotoxin tolerance. Plasma was collected at -1, -0.5, 0, 1, 2, 3, 4, 6, 8, and 24 h relative to each LPS administration. Rectal body temperature (BT) was measured before each blood sampling and at 5 and 7 h. Data were analyzed by repeated measures with sampling time as the repeated effect. Each genotype had at least one pro-inflammatory response that indicated it might have a more robust response than the other genotypes. The CH heifers had a greater TNF-α response, UH heifers had greater IL-6 and XO responses and CA heifers had greater BT and SAA response to LPS than the other genotypes. There was a genotype by time by interaction as cortisol peaked earlier in CH and UH than in CA heifers. Glucose response was less in CA and insulin response was greater in CH heifers. Endotoxin tolerance to LPS was evident as pro-inflammatory, cortisol, glucose and insulin responses were less during Challenge 2 than during Challenge 1. Differences among genotypes during Challenge 1 were eliminated during Challenge 2 except for the greater SAA response in CA heifers and indicate the potential for differential impacts of genotype on the development of endotoxin tolerance. Specific reasons for these effects of genotype are not clear from these data but the results support the hypothesis for differential innate immune signaling among these bovine genotypes.

Feed deprivation in Merino and Terminal sired lambs: (2) the metabolic response under pre-slaughter conditions and impact on meat quality and carcass yield

Under current Australian industry pre-slaughter guidelines, lambs may be off feed for up to 48 h before slaughter. The purpose of this study was to examine what proportion of circulating metabolites at slaughter are due to stress and feed deprivation and if this response differs between Merino and Terminal genotypes. In addition the effect of feed deprivation on carcass weight and meat quality was examined. Jugular blood samples were collected from 88 Merino and Terminal sired lambs at rest and at slaughter following 24, 36 and 48 h of feed deprivation and plasma analysed for glucose, lactate, non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHOB). From the same carcasses hot carcass weight (HCWT) were measured as well as a suite of meat quality traits measured such as M. longissimus lumborum (loin) and M. semitendinosus pH at 24 h postmortem. Loin samples were also analysed for intramuscular fat content and Warner-Bratzer Shear Force. Merino sired lambs had a higher NEFA response compared to Terminal sired lambs at slaughter after 24, 36 and 48 h of feed deprivation, with NEFA levels up to 35% higher than previously reported in the same animals at rest in animal house conditions, whereas BHOB response to feed deprivation was not affected by sire type (P>0.05) and similar to previously reported at rest. In addition to the metabolic effects, increasing feed deprivation from 36 h was associated with a 3% reduction in HCWT and dressing percentage as well as causing increased ultimate pH in the M. semitendinosus in Merino sired lambs. Findings from this study demonstrate that Merino and Terminal sired lambs differ in their metabolic response to feed deprivation under commercial slaughter conditions. In addition, commercial feed deprivation appears to have a negative effect on ultimate pH and carcass weight and warrants further investigation.

Feed efficiency and body composition are related to cortisol response to adrenocorticotropin hormone and insulin-induced hypoglycemia in rams

Metabolic rate and energy consumption increase through the activation of the hypothalamic-pituitary-adrenal axis when an animal is exposed to a stressor. Residual feed intake (RFI) as a measure of efficiency has been shown to be related to exogenous adrenocorticotropin hormone (ACTH)-stimulated cortisol concentrations, which is indicative of the relationship between an animal's response to stress and the efficiency with which the energy is used for growth and production. In this study, we tested the hypothesis that sheep with low post-ACTH serum cortisol concentration relative to the other sheep in the flock have lower RFI values and lower cortisol concentrations following insulin-induced hypoglycemia. Adrenocorticotropin hormone (2.0 microg/kg body weight)-stimulated cortisol concentrations were measured in 100 sheep. The extreme responders were selected (n = 12 high cortisol, n = 12 low cortisol), and feed efficiency and body composition parameters were measured. A second ACTH challenge and an insulin challenge were administered. More efficient sheep (more negative RFI value) were found to have lower (P < 0.05) cortisol concentrations following both an ACTH challenge and an insulin challenge. Low-cortisol sheep (low response to ACTH or insulin) were found to have a lower (P < 0.05) proportion of fat tissue in comparison to the high-cortisol animals. These data clearly indicate that an animal's response to exogenous ACTH or insulin-induced hypoglycemia as a stressor is related (P < 0.05) to efficiency of energy use when measured as RFI. These data have important implications in enabling identification of animals that are superior in terms of feed efficiency and for understanding the physiological mechanisms underlying efficiency of energy use.

Evaluation of a compartmental model to describe non-esterified fatty acid kinetics in Holstein dairy cows

The dynamics of non-esterified fatty acid (NEFA) metabolism in lactating dairy cows requires quantification if we are to understand how dietary treatments and disease influence changes in body condition (adipose reserves) and the production of milk fat. Recently, Thomaseth & Pavan (2003) presented a compartmental model (Thomaseth model), which employs the pattern of plasma insulin concentrations in humans to predict the dynamic changes that occur in the plasma concentrations of glucose and NEFA during an intravenous glucose tolerance test (IVGTT). The Thomaseth model, or at least a similar model, could have potential application to the field of energy metabolism in ruminants because it would enable the estimation of parameters that describe the rates of whole body disposition of glucose, and the production and utilization of NEFA. In this study we investigated the suitability of the Thomaseth model to describe NEFA and glucose kinetics in 10 lactating Holstein-Friesian cows given a standard IVGTT in early lactation. The Thomaseth model described the general pattern of the NEFA response and, in particular, described the downward-slope and nadir in NEFA concentrations reasonably well. However, it failed to describe the initial latency period (the period before NEFA concentrations decline precipitously), and it could not describe terminal ‘rebound’ plateau in NEFA concentration. Because of these inherent problems, the parameters of the Thomaseth model cannot be considered to provide accurate estimates of rates of NEFA production or utilization. It is concluded that the Thomaseth model is not suitable for describing NEFA kinetics in lactating dairy cows.

Effect of somatotropin on thyroid hormones and cytokines in lactating dairy cows during ad libitum and restricted feed intake

Twelve Holsteins in first lactation were used to investigate the relationship between energy balance and effects of bovine somatotropin (bST) on thyroid hormone metabolism and cytokine concentrations in serum. Six cows were fed for ad libitum intake and six cows were feed restricted to induce negative energy balance during two treatment periods of 6 d. During treatment periods, cows were administered vehicle or 40 mg of bST/d according to a crossover design. Between treatment periods was a 15-d recovery period, during which all cows were fed ad libitum. Cows that were fed ad libitum remained in positive energy balance during control and bST treatments, whereas cows that were fed for restricted intake were in negative energy balance during control and bST treatment periods. In both dietary groups, bST decreased energy balance. Milk production and the fat percentage of milk increased during bST treatment in both dietary groups. Fat-corrected milk yield was increased 13% by bST treatment. Serum concentrations of IGF-I did not differ between dietary groups but were greater during bST than control periods. Serum thyroxine concentration was decreased by bST treatment. Serum triiodothyronine and reverse-triiodothyronine were not altered by hormone treatment, but circulating concentrations of thyroid hormones were apparently reduced by dietary restriction. Neither hepatic nor mammary thyroxine 5'-deiodinase was affected by bST treatment. Plasma concentration of tumor necrosis factor-alpha, a potential regulator of thyroxine 5'-deiodinase, was not affected by bST treatment. Short-term treatment with bST did not influence thyroid hormone metabolism in lactating cows in positive or negative energy balance.

Somatotropin regulates adipose tissue metabolism in neonatal swine

Somatotropin (ST) reduces lipid deposition in growing and adult animals, but its effect in neonatal pigs is not clear. In this study, we tested the hypothesis that ST inhibits lipid deposition in neonatal pig adipose tissue. Four neonatal (2.9 +/- 0.1 kg, 7 d of age) and four growing (17.0 +/- 1.4 kg, 60 +/- 3 d of age) crossbred pigs were used. Subscapular adipose tissue fragments were cultured with or without ST (4.5 nmol/L) for 24 h in the absence or presence of insulin (7 nmol/L). After culture for 24 h with insulin alone, adipocytes from neonatal and growing pig adipose tissue maintained the capacity to incorporate glucose into total lipid at rates comparable to those in fresh tissue. Culture for 24 h with ST in the presence or absence of insulin decreased adipocyte glucose incorporation into fatty acids. Addition of ST, in the absence or presence of insulin, also increased the accumulation of glycerol in the medium during culture of neonatal and growing pig adipose tissue. Furthermore, culture for 24 h with ST resulted in higher basal lipolysis measured during incubation of isolated adipocytes in the presence of adenosine deaminase. In addition, culture with ST decreased adipose tissue lipoprotein lipase (LPL) activity and completely blocked the stimulatory effect of insulin on activity of this enzyme. The present study is the first to demonstrate in neonatal pigs that, as in growing pigs, ST regulates adipose tissue metabolism through decreasing lipid synthesis and LPL activity and increasing lipolysis. Thus, ST may play an important role in nutrient partitioning during the neonatal period.

Biology of somatotropin in growth and lactation of domestic animals

Impressive progress has been made during the past 15 years in our understanding of the biology of somatotropin (ST) in domestic animals. In part, this progress was sparked by advances in biotechnology that made feasible the production of large quantities of recombinant bovine ST (bST) and porcine ST (pST). The availability of recombinant bST and pST resulted in an exponential increase in investigations that explored their role in growth and lactation biology, as well as evaluated their potential for commercial use. Collectively, these studies established that administration of bST to lactating dairy cows increased milk yield, and treatment of growing pigs with pST markedly stimulated muscle growth and reduced fat deposition. In addition to these "efficacy" studies, a substantial number of investigations examined the mechanisms by which ST affects lactation and growth of domestic animals. This review summarizes the diverse physiological effects ST has on growth and lactation and discusses the underlying mechanisms that mediate these effects in domestic animals.