Effects of induced parturition and estradiol on feed intake, liver triglyceride concentration, and plasma metabolites of transition dairy cows

Endocrine Signals Altered by Heat Stress Impact Dairy Cow Mammary Cellular Processes at Different Stages of the Dry Period

Simple Summary

Late-gestation heat stress increases blood prolactin and decreases oestrogen concentrations in dry cows. These hormonal alterations may disturb mammary gland remodelling during the dry period, thereby being potentially responsible for the observed production impairments during the subsequent lactation. This project aimed to better understand the molecular mechanisms underlying subsequent impairments in mammary performance after dry period heat stress. For this, we studied the expression of genes encompassing prolactin and oestrogen pathways and key cellular process pathways under different thermal environments and in vitro hormonal milieus. The results of this study revealed that late-gestation heat stress impacted the expression of genes in the mammary gland involved in key cellular processes occurring during the dry period. Furthermore, our results indicated that these modifications are in part modulated by alterations of oestrogen and prolactin signalling.

Abstract

Hormonal alterations occurring under late gestation heat stress may disturb mammary gland remodelling, resulting in a reduced milk yield during the subsequent lactation. We investigated the effects of an altered endocrine environment on mammary gene expression at different stages of the dry period. Mammary gland biopsies from in vivo-cooled (CL) or heat-stressed (HT) cows were collected at d 3 and 35 relative to dry-off and divided into explants. Explants were incubated in vitro for 24 h in one of three media: Basal: no prolactin or estrogen; CL-mimic: Basal + low prolactin + high 17β-estradiol, or HT-mimic: Basal + high prolactin + low 17β-estradiol. Real time qPCR was used to quantify gene expression. We established that late-gestation heat stress changes the expression of prolactin and oestrogen receptors, downregulates genes involved in apoptosis, autophagy and proliferation at d 3 and upregulates genes related to those cellular processes at d 35. Moreover, compared with in vivo treatments, we showed that the expression of fewer genes was impacted by in vitro treatments which aimed to mimic the hormonal response of cows exposed to a different environment. Further research will continue to uncover the mechanisms behind the production impairments caused by late-gestation heat stress.

Traditional Chinese herbal medicine complex supplementation improves reproductive performance, serum biochemical parameters, and anti-oxidative capacity in periparturient dairy cows

This study was conducted to investigate the effects of a traditional Chinese herbal medicine complex (TCHMC) on the productive performance of periparturient dairy cows. Eighteen non-lactating pregnant Holstein dairy cows with similar body conditions with 1 to 2 parity were randomly divided into three groups (n = 6), receiving a basal diet with 0 (CON group), 200 (T-200 group), and 300 (T-300 group) g TCHMC per day from 14 to 9 days prepartum. The results demonstrated that TCHMC treatments decreased the days of gestation, calving to first service, and calving to first visible estrus. Compared with CON at specific time points, TCHMC treatments increased the concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E₂), whereas progesterone (P₄) and E₂ concentrations decreased. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and creatine kinase (CK) concentrations were downregulated, whereas that of globulin (GLB) and immunoglobulin G (IgG) were upregulated by TCHMC treatments around the time of calving. Compared with CON and T-200 treatments, the T-300 treatment increased the serum concentrations of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) and decreased the malondialdehyde (MDA) concentration from 7 d prepartum to 21 d postpartum when. In addition, although TCHMC treatment had no effect on average birth weight, heart rate, respiratory rate, and body temperature of calves, the T-300 treatment increased serum albumin (ALB) and IgG concentrations in calves from 3 to 14 days postpartum. The addition of TCHMC used in the present study could serve as a potential effective strategy to improve the health and productive performance of periparturient dairy cows, and the optimal dose should be set at 300 g per day.

Late gestation heat stress in dairy cows: Effects on dam and daughter

In dairy cattle, the final weeks before parturition are physiologically challenging and an important determinant of subsequent production performance. External stressors should be carefully managed during this period to avoid adding strain on the animals. Late-gestation heat stress impairs productivity in the dam and exerts transgenerational effects on progeny. Physiological responses are complex and detriments to performance are multifaceted. Late-gestation heat stress blunts mammary gland involution in the first half of the dry period and impairs cell proliferation as calving approaches. Moreover, cows that were exposed to prepartum heat-stress exhibit reduced adipose tissue mobilization and a lower degree of insulin resistance during early lactation. Prepartum heat exposure also depresses immune function and evidence links this decrease to altered prolactin signaling under heat stress. Placental functions are also impaired as reflected in a higher cotyledon mass but lower maternal circulating estrone sulfate concentrations, potentially resulting in lower nutrient supply and reduced calf birth weight. In addition, calves born to heat-stressed dams show impaired immune function and therefore higher disease susceptibly. Novel evidence reported that intrauterine heat stress alters the methylation profile of liver and mammary DNA, which may also contribute to the poorer performance during adulthood of calves exposed to heat stress in utero. Understanding the contribution of all altered biological systems during late-gestation heat stress can be used as a basis for improving cow management during the dry period. This article provides a review of the impacts of late-gestation heat stress and of the emerging understanding of the biological mechanisms that underlie the observed impairments of performance.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Late gestation heat stress of dairy cattle programs dam and daughter milk production

Anticipated increases in the world population to 9 billion people will lead to increased demand for food. Dairy products represent one of the most sustainable animal sources of food protein because ruminants can utilize byproduct and forage feeds unsuitable for human consumption. Continued improvements in productivity will depend on deeper understanding of the biology of lactation, including developmental programming of tissues critical to that process. Although prenatal programming of postnatal phenotype is well documented for growth, behavior, and disease, there may also be instances of "programming" that last for a specific physiological stage (e.g., lactation). We distinguish between these 2 terms by the use of developmental programming to describe a permanent effect, whereas the more general term is used to describe nonpermanent impacts on the mammary gland. Despite this complexity, here we review the evidence that exposure to elevated temperature and humidity during late gestation can program reduced yields in the subsequent lactation, largely through effects at the mammary gland. Furthermore, we provide emerging evidence that adult capacity for milk synthesis can be programmed in the calf that dam is carrying by events during fetal life occurring 2 yr before. Specifically, calves born to dams that are heat stressed for the final 6 wk of gestation produce 19% less milk in lactation relative to calves from dams provided with evaporative cooling. Importantly, the increased milk yield in animals derived from dams under evaporative cooling occurred without a greater decline in BW that accompanies negative energy balance during early lactation. Therefore, the increase in milk production suggests an increase in the efficiency of conversion of feed to milk. These data indicate that a brief period of heat stress late in development reduces the physiological efficiency of the cow in a coordinated manner to result in a substantial decline in productivity. It is likely that this programming effect would be observed across genetic lines and result in poor sustainability of milk production. Milk will continue to be an important source of high-quality, human-edible food and technologies that improve the efficiency of production will be critical to enhance sustainability. These data provide compelling support for the concept that programming impacts on the dam and the developing fetus will play a role in optimizing the efficiency of production.

Economic feasibility of cooling dry cows across the United States

Heat stress during the dry period reduces milk yield in the subsequent lactation of dairy cows. Our objectives were to quantify the economic losses due to heat stress if dry cows are not cooled and to evaluate the economic feasibility of dry cow cooling. We used weather data from the National Oceanic and Atmospheric Administration to calculate the number of heat stress days for each of the 50 US states. A heat stress day was declared when the daily average temperature-humidity index was ≥68. The number of dairy cows in each state in 2015 was obtained from the USDA-National Agricultural Statistics Service. We assumed that 15% of the cows were dry at any time, a 60-d dry period, and a calving interval of 400d. Only cows in their second or greater parity (65%) benefitted from cooling during the dry period of the previous parity. Milk yield decreased by 5kg in the subsequent lactation (340d) if the cow experienced heat stress during the dry period based on a review of the literature. The default marginal value of milk minus feed cost was $0.33/kg of milk. The investment analysis included purchases of fans and soakers and use of water and electricity. Investment in a dry cow barn was considered separately. The average US dairy cow would experience 96 (26%) heat stress days during the year if not cooled and loses 447kg of milk in the subsequent lactation if not cooled when dry. Annual losses would be $810 million if dry cows were not cooled ($87/cow per yr). For the top 3 milk-producing states (California, Wisconsin, New York), and Florida and Texas, the average milk losses in the subsequent lactation were 522, 349, 387, 1,197, and 904kg, and reduced profit per cow per year would be $101, $68, $75, $233, and $176, respectively. The average benefit-cost ratio and payback periods of cooling dry cows in the United States were 3.15 and 0.27 yr (dry cow barn already present) and 1.45 and 5.68 yr (if investing in a dry cow barn) in the default scenario. To reach positive net present values, 6d (barn is present) and 55d (barn investment necessary) of heat stress annually were necessary (default assumptions). Other benefits of cooling, such as increased health and more productive offspring, were not considered. In conclusion, cooling of dry cows was profitable for 89% of the cows in the United States when building a new barn is required (under default assumptions) and very profitable when construction of a dry cow barn is not required (except for Alaska).

Comparison of voluntary food intake, apparent digestibility, digesta kinetics and digestive tract content in Manchega and Lacaune dairy sheep in late pregnancy and early and mid lactation

Two experiments were carried out with pregnant (experiment 1) and lactating ewes (experiment 2), to compare dry-matter (DM) intake, and total tract apparent digestibility, digesta kinetics and weight of digestive tract contents of Lacaune and Manchega sheep, with the aim of explaining possible differences between the breeds in voluntary food intake. In experiment 1, 20 3-year-old single-bearing pregnant ewes, 10 Manchega and 10 Lacaune, were permanently housed for the last 10 weeks of pregnancy. The diet used consisted of lucerne hay, offeredad libitum, supplemented with 0·3 kg/day of concentrate. DM and digestible DM intake per kg M0·75were higher (P< 0·01) in Lacaune than in Manchega sheep. Breed did not affect total tract apparent digestibility, fractional rates of passage, transit time, total mean retention time, or weight of digestive tract contents. Changes in body weight and body condition score were similar between breeds. In contrast, Lacaune lambs tended (P= 0·09) to weigh less than Manchega lambs, suggesting genetic differences in the energy utilization between breeds in late pregnancy. Higher DM intake observed in Lacaune sheep may have been related to a higher energy demand for mammary development. In experiment 2, 32 3-year-old lactating multiparous ewes, 16 Manchega and 16 Lacaune, were permanently housed during the first 12 weeks of lactation. The experimental diet used was based on a mixture of maize silage and dehydrated lucerne (10: 1, fresh weight basis), offeredad libitum, and supplemented with 0·8 kg/day of concentrate. Milk, fat and protein yield as well as DM and digestible DM intake in Lacaune ewes was higher (P< 0·01) than in Manchega ewes. DM intake was constant in Lacaune sheep with advancing lactation, while in Manchega sheep DM intake decreased. Throughout this period Lacaune ewes lost 0·5 kg of body weight while Manchega gained 4·4 kg. Breed did not affect either apparent digestibility of DM, organic matter and neutral-detergent fibre, or fractional rates of passage, transit time and total mean retention time. The weight of total tract digestive contents was greater (P< 0·05) in Lacaune than in Manchega sheep, particularly in the reticulo-rumen. Results suggest that the scheme of selection in Lacaune dairy sheep has increased milk yield together with voluntary food intake, the latter being associated with an increase in the rumen fill capacity. The higher milk yield of Lacaune ewes cannot be attributed to the higher DM intake only; other factors, i.e. mobilization of fat reserves, are required to support this higher milk output.

Effect of heat stress during the dry period on mammary gland development

Heat stress during the dry period negatively affects hepatic metabolism and cellular immune function during the transition period, and milk production in the subsequent lactation. However, the cellular mechanisms involved in the depressed mammary gland function remain unknown. The objective of the present study was to determine the effect of heat stress during the dry period on various indices of mammary gland development of multiparous cows. Cows were dried off approximately 46 d before expected calving and randomly assigned to 2 treatments, heat stress (HT, n=15) or cooling (CL, n=14), based on mature equivalent milk production. Cows in the CL treatment were provided with sprinklers and fans that came on when ambient temperatures reached 21.1°C, whereas HT cows were housed in the same barn without fans and sprinklers. After parturition, all cows were housed in a freestall barn with cooling. Rectal temperatures were measured twice daily (0730 and 1430 h) and respiration rates recorded at 1500 h on a Monday-Wednesday-Friday schedule from dry off to calving. Milk yield and composition were recorded daily up to 280 d in milk. Daily dry matter intake was measured from dry off to 42 d relative to calving. Mammary biopsies were collected at dry off, -20, 2, and 20 d relative to calving from a subset of cows (HT, n=7; CL, n=7). Labeling with Ki67 antigen and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling were used to evaluate mammary cell proliferation and apoptosis, respectively. The average temperature-humidity index during the dry period was 76.6 and not different between treatments. Heat-stressed cows had higher rectal temperatures in the morning (38.8 vs. 38.6°C) and afternoon (39.4 vs. 39.0°C), greater respiration rates (78.4 vs. 45.6 breath/min), and decreased dry matter intake (8.9 vs. 10.6 kg/d) when dry compared with CL cows. Relative to HT cows, CL cows had greater milk production (28.9 vs. 33.9 kg/d), lower milk protein concentration (3.01 vs. 2.87%), and tended to have lower somatic cell score (3.35 vs. 2.94) through 280 d in milk. Heat stress during the dry period decreased mammary cell proliferation rate (1.0 vs. 3.3%) at -20 d relative to calving compared with CL cows. Mammary cell apoptosis was not affected by prepartum heat stress. We conclude that heat stress during the dry period compromises mammary gland development before parturition, which decreases milk yield in the next lactation.

Relationship between serum nonesterified fatty acids at calving and the incidence of periparturient diseases in Holstein dairy cows

The objective was to describe the relationship between concentration of serum nonesterified fatty acids (NEFAs) at calving and the incidence of periparturient disorders in Chilean Holstein dairy cows (Bos taurus). The study was conducted at two dairies (central Chile) with 700 milking cows each and similar management. Between July 2006 and March 2007, 350 cows were selected, and concentrations of serum NEFAs were determined at calving. The incidence of milk fever (MF), retained fetal membranes (RFMs), metritis, and clinical mastitis from calving to 100 d in lactation were consistently recorded. The relationship between concentration of serum NEFAs at calving and the incidence of periparturient diseases was determined using logistic regression. The main explanatory variable was concentration of serum NEFAs at calving. The incidence of MF, RFM, metritis, and mastitis was 5.4%, 15.6%, 10.8%, and 14.4%, respectively. There was no association between concentration of NEFAs at calving and the incidence of these conditions when the median value of NEFAs (0.9 mEq/L) was used as a cutoff. However, when the 75th percentile (1.2 mEq/L) was used as the cutoff, cows with values <1.2 mEq/L were 0.45 and 0.32 times as likely to develop clinical mastitis and MF, respectively, compared with cows with values >or=1.2 mEq/L. When the 90th percentile (1.6 mEq/L) was used as a cutoff, cows with values <1.6 mEq/L were 0.25 times as likely to develop clinical mastitis compared with cows with values >or=1.6 mEq/L. As a continuous variable, for every 0.1 mEq/L increment in NEFAs at calving, cows were 1.11 times more likely to experience clinical mastitis. In conclusion, cows with NEFA concentrations >or=1.2 mEq/L had a higher incidence of clinical mastitis and MF than that of cows with values <1.2 mEq/L.

Effect of melatonin on biochemical variables of the blood in dairy cows

In order to examine the effect of exogenous melatonin on selected biochemical variables of the blood in ruminants, dairy cows were given the pineal gland hormone in the dose of 0.1 mg/kg body weight. One and four hours after melatonin administration blood samples were collected from the cows in the control and the treated group in order to determine the levels of glucose, insulin, total cholesterol, triglycerides, free fatty acids, as well as the activities of alanine and aspartate aminotransferase. The pineal gland hormone caused a significant increase in the levels of total cholesterol and triglycerides, slight increases in glucose and insulin levels, and a significant decrease in the concentration of free fatty acids. Melatonin did not exert an effect on the activity of liver enzymes.

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.

Transition cow: interaction with fertility

In recent years a progressive worsening of fertility indices in dairy cow herds has been observed. Several factors (genetic, dietary and management) seem to be more related to poor fertility than milk yield level. The degree and the length of the energy deficit during the transition period are inversely related to reproductive indices (e.g. conception rate is <30% for BCS decreases over one unit). A serious energy deficit reduces (or suppresses) pulsatile secretion of gonadotrophins (ovarian dysfunction and/or smaller follicles): IGF-I and insulin plasma levels (slower follicle growth and higher embryonic mortality); and progesterone production from the corpus luteum (higher rate of embryonic abortions). The diet influences fertility in several ways. Excess of rumen degradable proteins, apart from negative energy balance, negatively affects reproductive activity. Conversely, some nutrients (i.e. some polyunsaturated fatty acids or some amino acids) seem to show positive effects on fertility. Finally, the relationship between health status, often compromised during the transition period, and fertility efficiency is discussed. The release of cytokines seems to be related directly and indirectly (mainly by the change in usual hepatic metabolism to the malfunction of reproductive apparatus. Quick recovery of reproductive activity requires the adoption of strategies around calving to cover the higher environmental and nutritive requirements and to prevent disorders of any kind.

Changes in hepatic microsomal triglyceride transfer protein and triglyceride in periparturient dairy cattle

We determined the relationship between microsomal triglyceride transfer protein (MTP) (activity, mass, and mRNA) and liver triglyceride concentration in 16 dairy cows (13 multiparous and three primiparous) from 27 d before expected calving (d -27) to 35 d postpartum (d 35), the time period when fatty liver is most likely to develop. In addition, dry matter intake, plasma nonesterified fatty acids (NEFA), and plasma glucose were monitored. There were no significant parity x time interactions. Dry matter intake, plasma NEFA, plasma glucose, and liver triglyceride were significantly affected by day of sampling. Dry matter intake was 10.7, 8.0, and 19.5 kg/d on d -27, 2, and 35, respectively. Plasma NEFA concentration was higher on d 2 (1113 microEq/L) compared with d -27 (201 microEq/L) and 35 (358 microEq/L). Plasma glucose concentration was 63.3, 54.3, and 57.8 mg/dl on d -27, 2, and 35, respectively. Hepatic triglyceride (TG) concentration increased from 1.8 to 11.8% liver TG (DM basis) on d -27 and 2, respectively. There was no difference between hepatic triglyceride concentration on d 2 and 35. There was a significant effect of day of sampling on hepatic MTP activity and mRNA. Hepatic MTP activity decreased from 2.08 to 1.79 nmole triolein transferred/ h per mg of microsomal protein on d -27 and 2, respectively, and increased from 1.79 to 2.17 nmole triolein transferred/h per mg of microsomal protein on d 2 and 35, respectively. Hepatic MTP mRNA increased from d -27 to 2 and remained elevated from d 2 to 35. There was no effect of day of sampling on MTP mass. There were no significant correlations between hepatic MTP activity, mass, or mRNA with either liver TG or plasma NEFA on any of the sampling days. The cause of a decrease in hepatic MTP activity and increase in mRNA on d 2 is unknown. However, the lack of correlation between MTP activity, mass, or mRNA with either liver TG or plasma NEFA on d 2 postpartum suggests that MTP probably does not play a role in the etiology of fatty liver that occurs in dairy cows at calving.