Relationships between thyroid hormones and serum energy metabolites with different patterns of postpartum luteal activity in high-producing dairy cows

This study investigated the relationships of thyroid hormones, serum energy metabolites, reproductive parameters, milk yield and body condition score with the different patterns of postpartum luteal activity in the postpartum period. A total of 75 multiparous healthy (free of detectable reproductive disorders) Holstein dairy cows (mean peak milk yield = 56.5 ± 7.0 kg/day) were used in this study. Transrectal ultrasound scanning and blood sample collection were performed twice weekly. Serum concentrations of progesterone (P₄) were measured twice weekly and beta-hydroxybutyrate (BHBA), non-esterified fatty acids, thyroxine (T₄), 3,30,5-tri-iodothyronine (T₃), free thyroxine (fT₄) and free 3,30,5-tri-iodothyronine (fT₃) were measured every 2 weeks from the 1st to the 8th week postpartum. On the basis of the serum P₄ profile of the cows, 25 (33.4%) had normal luteal activity (NLA), whereas 30 (40%), 10 (13.3%), 6 (8%) and 4 (5.3%) had prolonged luteal phase (PLP), delayed first ovulation (DOV), anovulation (AOV) and short luteal phase, respectively. Serum T₄ concentrations in PLP cows were higher than that in NLA cows at the 3rd week postpartum and did not change during the period of study, whereas in the NLA cows the concentrations increased (P < 0.05). Further, the least square (LS) mean of serum fT₄ concentrations in the DOV and AOV cows were significantly lower than in the NLA cows during the study period (P < 0.05). In addition, the AOV cows had higher LS mean serum BHBA and T₄ concentrations than the NLA cows in early weeks postpartum (P < 0.05). In conclusion, the serum thyroid hormones’ profile differs in high-producing dairy cows showing PLP, AOV and DOV in comparison with the postpartum NLA cows.     

Increased body condition score through increased lean muscle,but not fat deposition,is associated with reduced reproductive response to oestrus induction in beef cows

Energy reserve, estimated as body condition score (BCS), is the major determinant of the re-initiation of ovarian activity in postpartum cows. Leptin, IGF-I and insulin are positively related to BCS and are putative mediators between BCS and reproductive function. However, when BCS and body composition dissociates, concentrations of these metabolic hormones are altered. We hypothesized that increasing lean muscle tissue, but not fat tissue, would diminish the reproductive response to oestrus induction treatments. Thirty lactating beef cows with BCS of 3.10±1.21 and 75.94±12 days postpartum were divided in two groups. Control cows (n=15) were supplemented with 10.20 kg of concentrate daily for 60 days. Treated cows (n=15) were supplemented equally, and received a β-adrenergic receptor agonist (β-AA; 0.15 mg/kg BW) to achieve accretion of lean tissue mass and not fat tissue mass. Twelve days after ending concentrate supplementation/β-AA treatment, cows received a progestin implant to induce oestrus. Cows displaying oestrus were inseminated during the following 60 days, and maintained with a fertile bull for a further 21 days. Cows in both groups gained weight during the supplementation period (Daily weight gain: Control=0.75 kg v. β-AA=0.89 kg). Cows treated with β-AA had a larger increase in BCS (i.e. change in BCS: control=1 point (score 4.13) v. β-AA=2 points (score 5.06; P<0.05), as a result of muscle accretion (i.e. change in muscle depth: control 0.21 cm v. β-AA 0.97 cm; P<0.05) but not adipose tissue (i.e. change in back fat depth; control 0.13 cm v. β-AA −0.06 cm; P<0.05). The changes in body composition in β-AA cows were associated with a reduction in serum concentrations of IGF-I (25.4%) and leptin (27.9%), without observed changes in insulin. Ovulation and pregnancy to 1st service (P>0.05) did not differ between groups. However, the number of cows displaying oestrus (control 13/15 v. β-AA 8/15; P<0.05) and the percentage cycling (control 6/8 v. β-AA 3/10; P=0.07) after progestin treatment and the pregnancy percentage at the end of the breeding period (control 13/15 v. β-AA 8/15; P<0.05) were lower in β-AA than control cows. In summary, the increase BCS through muscle tissue accretion, but not through fat tissue accretion, resulted in a lower response to oestrus induction, lower percentage of cycling animals and lower pregnancy percentage after progestin treatment; which was associated with a decrease in serum concentrations of leptin and IGF-I.     

Low peripheral progesterone and late embryonic/early fetal loss in suckled beef and lactating dairy cows

Pregnancy failure during placentation in lactating dairy cows was associated with low concentrations of serum progesterone. Beef cows have greater serum progesterone and less pregnancy failure. Experiment 1 determined that reduction of serum progesterone affected late embryonic/early fetal loss in suckled beef cows. Cows (n = 40) received progesterone from two new or used controlled internal drug releasing devices, replaced every 5 d, beginning on Day 28 of gestation (mating = Day 0); CL were enucleated on Day 29. Retention of pregnancy was 77% in treated cows and 97% in 78 control cows (P < 0.05). Experiment 2 determined how pregnant, lactating dairy cows with high or low progesterone concentrations during Days 28-34 differed in luteal function or in serum progesterone during replacement therapy. Luteal tissue from such cows was assayed for progesterone and expression of mRNA for genes of endothelin and prostaglandin (PG) systems. Secretion of progesterone and prostaglandins by dispersed luteal cells was determined during incubation with LH, endothelin-1, or arachidonic acid. Neither luteal progesterone nor mRNAs for endothelin or prostaglandin systems differed. Endothelin-1 inhibited secretion of progesterone more (P < 0.05) in luteal cells from cows with low versus high serum progesterone, when incubated with arachidonic acid. Secretion of prostaglandin F₂α was increased and that of 6-keto-PGF₁α decreased by endothelin-1 in vitro. Serum progesterone during replacement was lower (P < 0.05) for cows with low than high serum progesterone at lutectomy. Thus, clearance, more than luteal production, determined peripheral progesterone in pregnant, lactating dairy cows.     

Effects of using vasectomized bulls in artificial insemination practice on the reproductive efficiency of Italian buffalo cows

The effects of the presence or absence of vasectomized male buffaloes on the reproductive efficiency of buffalo cows (n = 396) undergoing artificial insemination (AI) was studied on six farms owned and operated by a single consortium. Lactating animals were separated into two groups of various sizes on each farm and kept under semi-range conditions. Vasectomized bulls were present in one group at a bull/empty-cow ratio of 1:30. No bulls were present in the other group. Reproductive efficiency between the two groups over a period of 3.5 months was compared and evaluated on the basis of: 1) the number of spontaneous overt estruses associated with either feeble or intense signs of estrous behaviour; 2) the number of functional estrous cycles, i.e. estrous cycles with luteal phases defined as normal, based on specified progesterone concentrations in milk or blood plasma 8–10 days after estrus; 3) the number of consecutive functional estrous cycles in cases of induced estrus; and 4) pregnancy rate.Groups with bulls present demonstrated a significantly higher reproductive efficiency than groups without them. There was a higher incidence of spontaneous estrus (92 versus 69%; P < 0.01); spontaneous estrus of high intensity (62.2 versus 31.1%; P < 0.01); and higher incidence of functional estrous cycles following both spontaneous (65.8 versus 57.1%) and induced (77.0 versus 59.5%; P < 0.05) estrus. Exposure to vasectomised bulls also increased the incidence of consecutive functional estrous cycles (90.5 versus 68.1%; P < 0.01), and the pregnancy rate in cows inseminated at spontaneous (42.5 versus 18.9%; P < 0.01) or induced (51.1 versus 33.3%; P < 0.05) estrus. Overall pregnancy rate did not differ significantly between cows inseminated at induced or spontaneous estrus, although in the absence of bulls, pregnancy rate per AI was higher in cows inseminated at induced than at spontaneous estrus (33.3 versus 18.9%).     

Minimal progesterone concentration required for embryo survival after embryo transfer in lactating Holstein cows

Objectives were to determine progesterone concentration (P4) from days 4 to 28 relative to presumptive estrus necessary for maintenance of pregnancy in lactating Holstein cows. Cows were assigned to the low P4 (LowP4, n = 28) or control (n = 153) treatments. All cows were presynchronized with two injections of PGF_2α (14 d apart) and an ovulation synchronization protocol (11 d later; GnRH on day −10, PGF_2α on day −3; and GnRH on day 0 = presumptive estrus). Cows in the Low P4 treatment received 2 injections of prostaglandin F_2α on days 4 and 5 (day 0 = presumptive estrus) and a new CIDR insert on day 5 that was replaced every 7 d until day 28. Blood was sampled on days −9, −2, 0, 4, 7,14, 21, and 28. Ovaries were examined with ultrasound on days −9, −3, and 7 and cows bearing a corpus luteum ≥20 mm on day 7 received an embryo. On days 0, 4 and 7 P4 did not differ (P ≥ 0.27) but control cows had greater (P < 0.01) P4 on days 14, 21, and 28. Progesterone concentration fold change from day 0 to 7 was not (P = 0.14) affected by treatment, but P4 concentration fold change from day 7 to 14 was (P < 0.01) greater for control cows compared with LowP4 cows. No LowP4 cows became pregnant after embryo transfer, whereas 35.7, 25.5, and 21.4% of control cows were pregnant on day 28, 42, and 63, respectively. Progesterone concentration fold changes from day 0 to 7 (P = 0.03) and from day 7 to 14 (P = 0.05) were associated with pregnancy outcomes on day 63. Among cows that were pregnant on day 63, the minimum P4 concentration fold changes from day 0 to 7 and from day 7 to 14 were 2.71 and 1.48, respectively. Interestingly, cows with P4 concentration <5 ng/mL on day 14 were (P = 0.01) and tended to be (P = 0.07) more likely to lose pregnancy from day 28 to 42 and from day 28 and 63, respectively. Faster rise in P4 concentration during the metestrus and early diestrus are associated with pregnancy establishment following embryo transfer, which suggests that early rise in P4 concentration has an indirect effect on embryo development through modulation of uterine environment and secretion of histotroph. Furthermore, the positive effects of early rise in P4 concentration appear to go beyond the phase of maternal recognition of pregnancy through adhesion and placentation stages.     

Management practices associated with reproductive performance in Holstein cows on large commercial dairy farms

As a result of the increase in herd size and the intensification of production, the complexity of reproductive management has been growing in dairy herds. The aim of our study was to examine the associations of management practices and reproductive performance in Holstein cows on large commercial dairy farms. Management practices applied to cows were surveyed between 22 May and 6 November 2015 in 34 large Holstein-Friesian dairy herds in Hungary. Individual data of 23 784 cows that calved between 1 January 2014 and 31 December 2014 in the surveyed herds were gathered. Associations between the management practices and the reproductive parameters were analyzed by mixed effects models. Regarding heat abatement we found that ventilation with sprinklers was associated with the shortest breeding interval (P<0.01), the shortest calving to conception interval (P<0.01), and the highest odds of being pregnant by 200 days in milk (P<0.01). Solely ventilation showed similar (P>0.05) results to lack of heat stress protection. It was also revealed, that lack of a well-established voluntary waiting period (VWP) or a VWP shorter than 50 days was associated with less days to first service (P<0.01), shorter breeding interval (P<0.01) and calving to conception interval (P<0.05), as well as higher odds of carrying a calf by 200 days in milk (P<0.01) compared with those using a VWP of at least 50 days. Those farms that applied transrectal ultrasonography were more likely to use ventilation with sprinklers (P<0.05), hormonal synchronization (P<0.01) and to perform early pregnancy diagnosis followed by pregnancy recheck (P<0.05). The application of transrectal ultrasonography with one of the aforementioned practices was associated with reduced days to first service (P<0.05), shorter breeding interval (P<0.05) and higher odds of pregnancy at 200 days in milk (P<0.05). Our study highlights the management practices most closely related to improved reproductive performance, which are, therefore, suggested to be applied on dairy farms, considering the local circumstances of the individual farms.     

Incorporation of a rapid pregnancy-associated glycoprotein ELISA into a CIDR-Ovsynch resynchronization program for a 28 day re-insemination interval

The objective was to compare two resynchronization programs; one that used a blood-based ELISA for pregnancy-associated glycoproteins (PAG) for pregnancy diagnosis so that non-pregnant cows were re-inseminated at 28 d after first TAI, and another that used transrectal ultrasonography for pregnancy diagnosis so that non-pregnant cows were re-inseminated at 35 d after first TAI. The PAG_resynch cows (n = 103) began CIDR-Ovsynch resynchronization on Day 18 after first TAI (Day 0). On Day 25, the CIDR was removed and pregnancy diagnosis with a PAG ELISA was performed. If a cow was not pregnant on Day 25, she was treated with PGF_2α, treated with GnRH 2 d later (Day 27), and TAI on Day 28. Control cows (n = 99) were observed for estrus until Day 25, when they began an identical CIDR-Ovsynch program with pregnancy diagnosis by transrectal ultrasonography on Day 32. If a cow was not pregnant on Day 32, then she was treated with PGF_2α, treated with GnRH 2 d later (Day 34), and TAI on Day 35. There was no difference in pregnancy per AI (P/AI) for either group at first or second insemination. For cows without pregnancy loss, the interval between first and second (P < 0.001) or second and third (P < 0.016) TAI was shorter for PAG_resynch cows compared with Control cows. The interval between first and second or second and third TAI was not different if pregnancy loss cows were included in the analysis. Plasma progesterone concentrations were similar at PGF_2α treatment, and plasma estradiol concentrations increased similarly after PGF_2α treatment for PAG_resynch and Control cows. In conclusion, the 28 d CIDR-Ovsynch resynchronization protocol was comparable to a 35 d CIDR-Ovsynch resynchronization protocol that also included estrus detection. Shortened resynchronization protocols that do not require estrus detection may improve reproductive efficiency in dairy cattle.     

Effects of polyunsaturated fatty acids supplementation on reproductive parameters associated with the performance of suckled beef cows

To evaluate the effects of a polyunsaturated fatty acids (PUFA) supplement on reproductive parameters of suckled beef cows, two experiments were conducted. In Experiment (Exp.) 1, 60 primiparous cows were randomly assigned to one of two treatments: CTRL – 1.36 kg/day of corn gluten feed (CGF) and MEGR – 1.36 kg/day of CGF and 0.23 kg/day of calcium salts of soybean oil. Supplementation occurred from 30 days before fixed-time artificial insemination (TAI) until 7 days post-TAI. The expression of interferon-stimulated genes (ISG) was measured on days 18 and 21. Pregnancy rates were diagnosed on days 30 and 100. Treatment altered plasma fatty acid profile (P<0.05), however, did not change cow BW (P=0.52) or body condition score (BCS) (P=0.52). Treatment did not alter (P=0.12) pregnancy rates to TAI or final pregnancy rates (P=0.56). Treatments did not impact messenger RNA (mRNA) expression of the ISG OAS1 or MX2 on days 18 (P=0.67; P=0.96, respectively) or 21 (P=0.72; P=0.17, respectively). Length of gestation was greater (P=0.02) for MEGR, however, treatments did not alter calf birth weight (P=0.20). In Exp. two, 66 multiparous cows were assigned to one of two treatments: MEG – 0.65 kg/day of CGF+0.23 kg/day of calcium salts of palm oil and MEGR – 0.65 kg/day of CGF+0.23 kg/day of Ca salts of soybean oil. Cows were supplemented from 30 days prepartum to 30 days postpartum. On day 35 after TAI, pregnancy status, embryo crown-to-rump length (CRL), and plasma concentrations of pregnancy-specific protein-B (PSPB) were evaluated. Treatment altered plasma fatty acid profile (P<0.05). In addition, cows from the MEG treatment had greater BW (P<0.01) and BCS (P<0.01) than those in the MEGR treatment, as well as heavier calves at weaning (P=0.03). Treatment did not affect resumption of estrous cycle (P=0.29). There were no differences in pregnancy rates to TAI (P=0.87) or final pregnancy rates (P=0.29). No differences between treatments were detected on CRL (P=0.24) and plasma concentrations of PSPB (P=0.46). Birth weight (P=0.12) and calving distribution (P=0.52) were not altered. We concluded that PUFA supplementation altered plasma fatty acid profile, however, did not impact the remaining reproductive parameters evaluated.     

Added dietary cobalt or vitamin B12, or injecting vitamin B12 does not improve performance or indicators of ketosis in pre- and post-partum Holstein-Friesian dairy cows

Vitamin B₁₂ is synthesised in the rumen from cobalt (Co) and has a major role in metabolism in the peri-paturient period, although few studies have evaluated the effect of the dietary inclusion of Co, vitamin B₁₂ or injecting vitamin B₁₂ on the metabolism, health and performance of high yielding dairy cows. A total of 56 Holstein-Friesian dairy cows received one of four treatments from 8 weeks before calving to 8 weeks post-calving: C, no added Co; DC, additional 0.2 mg Co/kg dry matter (DM); DB, additional 0.68 mg vitamin B₁₂/kg DM; IB, intra-muscular injection of vitamin B₁₂ to supply 0.71 mg/cow per day prepartum and 1.42 mg/cow per day post-partum. The basal and lactation rations both contained 0.21 mg Co/kg DM. Cows were weighed and condition scored at drying off, 4 weeks before calving, within 24 h of calving and at 2, 4 and 8 weeks post-calving, with blood samples collected at drying off, 2 weeks pre-calving, calving and 2, 4 and 8 weeks post-calving. Liver biopsy samples were collected from all animals at drying off and 4 weeks post-calving. Live weight changed with time, but there was no effect of treatment (P>0.05), whereas cows receiving IB had the lowest mean body condition score and DB the highest (P<0.05). There was no effect of treatment on post-partum DM intake, milk yield or milk fat concentration (P>0.05) with mean values of 21.6 kg/day, 39.6 kg/day and 40.4 g/kg, respectively. Cows receiving IB had a higher plasma vitamin B₁₂ concentration than those receiving any of the other treatments (P<0.001), but there was no effect (P>0.05) of treatment on homocysteine or succinate concentrations, although mean plasma methylmalonic acid concentrations were lower (P=0.019) for cows receiving IB than for Control cows. Plasma β-hydroxybutyrate concentrations increased sharply at calving followed by a decline, but there was no effect of treatment. Similarly, there was no effect (P>0.05) of treatment on plasma non-esterified fatty acids or glucose. Whole tract digestibility of DM and fibre measured at week 7 of lactation were similar between treatments, and there was little effect of treatment on the milk fatty acid profile except for C15:0, which was lower in cows receiving DC than IB (P<0.05). It is concluded that a basal dietary concentration of 0.21 mg Co/kg DM is sufficient to meet the requirements of high yielding dairy cows during the transition period, and there is little benefit from additional Co or vitamin B₁₂.     

Effect of perennial ryegrass (Lolium perenne L.) cultivars on the milk yield of grazing dairy cows

The objective of this experiment was to investigate the effect of four perennial ryegrass cultivars: Bealey, Astonenergy, Spelga and AberMagic on the milk yield and milk composition of grazing dairy cows. Two 4 × 4 latin square experiments were completed, one during the reproductive and the other during the vegetative growth phase of the cultivars. Thirty-two Holstein–Friesian dairy cows were divided into four groups, with each group assigned 17 days on each cultivar during both experiments. Within each observation period, milk yield and milk composition, sward morphology and pasture chemical composition were measured. During the reproductive growth phase, organic matter digestibility (OMD) was greater for Bealey and Astonenergy (P < 0.001; +1.6%). AberMagic contained a higher stem proportion (P < 0.01; +0.06) and a longer sheath height (P < 0.001; +1.9 cm). Consequently, cows grazing AberMagic recorded a lower milk yield (P < 0.001; −1.5 kg/day) and a lower milk solids yield (P < 0.001; −0.13 kg/day). During the vegetative growth phase, OMD was greater (P < 0.001; +1.1%) for Bealey, whereas the differences between the cultivars in terms of sward structure were smaller and did not appear to influence animal performance. As a result, cows grazing Bealey recorded a higher milk yield (P < 0.001; +0.9 kg/day) and a higher milk solids yield (P < 0.01; +0.08 kg/day). It was concluded that grass cultivar did influence milk yield due to variations in sward structure and chemical composition.     

Effects of resynchronization strategies for lactating Holstein cows on pattern of reinsemination, fertility, and economic outcome

The objectives were to evaluate the pattern of re-insemination, pregnancy outcomes to re-insemination in estrus and at fixed time, and economic outcomes of lactating Holstein cows submitted to three resynchronization protocols. Cows were enrolled in the Experiment at 32 ± 3 d after pre-enrollment Artificial Insemination (AI), 7 d before pregnancy diagnosis, and randomly assigned to three resynchronization protocols. All cows diagnosed not pregnant at 39 ± 3 d after pre-enrollment AI were submitted to the Cosynch72 (Day 0 GnRH, Day 7 prostaglandin F_2α, and Day 10 GnRH and fixed time AI). Cows assigned to the control treatment received no further treatment, cows assigned to the GGPG treatment received a GnRH injection on Day −7, and cows assigned to the CIDR treatment received a controlled internal drug release (CIDR) insert containing 1.38 g of progesterone from Days 0-7. Cows observed in estrus were re-inseminated on the same day. Pregnancy was diagnosed at 39 ± 3 and 67 ± 3 d after re-insemination. Costs of the resynchronization protocols were calculated for individual cows enrolled in the study and pregnancies generated were given a value of $275. The GGPG treatment resulted in the slowest (P ≤ 0.06) rate of re-insemination. Overall pregnancy per AI (P/AI) at 39 ± 3 (P = 0.50) and 67 ± 3 (P = 0.49) d after re-insemination were not affected by treatment. Although cost of the control protocol was (P < 0.01) the smallest, return per cow resynchronized was (P < 0.01) greater for GGPG and CIDR protocols. We concluded that presynchronizing the estrous cycle of cows with GnRH or treating cows with a CIDR insert during resynchronization altered the pattern of re-insemination and improved the economic return of resynchronized cows.     

Estrous expression during a fixed-time artificial insemination protocol enhances development and interferon-tau messenger RNA expression in conceptuses from Bos indicus beef cows

Expression of estrus (EST) near the time of fixed-time artificial insemination (FTAI) increases pregnancy success in beef females. This outcome has been associated with improved pregnancy establishment and maintenance, although research is still warranted to validate this theory. Hence, this experiment compared ovarian, uterine and conceptus factors associated with pregnancy establishment in Bos indicus beef cows according to estrous expression during a FTAI protocol. One hundred lactating multiparous Nelore cows received a 2 mg injection of estradiol benzoate and an intravaginal progesterone (P4) releasing device on day −11, a 12.5 mg injection of prostaglandin F_2α on day −4, P4 device removal in addition to 0.6 mg injection of estradiol cypionate and 300 IU injection of equine chorionic gonadotropin on day −2, and FTAI on day 0. An estrous detection patch was attached to the tailhead of each cow on day −2, and estrous expression was defined as removal of >50% of the rub-off coating from the patch at FTAI. Overall, 39 cows expressed EST, 55 did not express EST (NOEST), and six cows lost their patch and were discarded from the experiment. Ovarian ultrasonography was performed at FTAI, and on days 7 and 15 of the experiment. Blood samples were also collected on days 7 and 15. Only cows without a corpus luteum (CL) on day 0, and with a CL on days 7 and 15 remained in the experiment (EST, n=36; NOEST, n=48). On day 15, cows were randomly selected within each group (EST, n=29; NOEST, n=30) for conceptus collection via transcervical flushing, followed by endometrial biopsy in the uterine horn ipsilateral to the CL. Within cows not assigned to conceptus collection, blood samples were collected for whole blood RNA extraction (day 20) and pregnancy status was verified by transrectal ultrasonography (day 30). Diameter of dominant follicle on day 0 and plasma P4 concentrations on day 7 were greater (P⩽0.02) in EST v. NOEST cows. Conceptus length and messenger RNA (mRNA) expression of prostaglandin E synthase and interferon-tau were greater (P⩽0.04) in EST v. NOEST cows. Moreover, EST cows diagnosed as pregnant on day 30 had greater (P<0.01) blood mRNA expression of myxovirus resistance 2 on day 20 compared with NOEST. In summary, estrous expression near the time of FTAI enhanced pregnancy establishment factors in B. indicus cows, including conceptus development and mRNA expression of interferon-tau.     

The Influence of Human Growth Hormone (GH) and Thyroxine (T4) on the Differentiation of Adipose Tissue in the Fetus

Late term fetuses from genetically obese dams have slightly larger fat cells, greater adipose tissue lipoprotein lipase (LPL) activities, elevated levels of thyroid hormones, and depressed growth hormone (GH) levels when compared to fetuses from lean dams. We have investigated the influence of thyroid hormone and GH status per se on these and other adipose tissue traits by chronically treating hypophysectomized (hypox) fetuses (day 70) between day 90 and 105 of gestation with either thyroxine (T4) or human GH. Treatment with T4 decreased body weights (P<.05), increased serum T₄ levels (P<.05), and enhanced skin and hair development (P<.05). Quantitative analysis of sections of perirenal and subcutaneous adipose tissue indicated that T₄ increased LPL activity (P<.05), slightly increased fat cell size, and more than doubled (P<.05) lipid accretion. A hypox induced deficit in fat cell cluster number in the outer layer of subcutaneous tissue was normalized by T₄ (P<.05). Conversely, human GH (hGH) treatment had no influence on body weight, increased serum hGH levels, decreased fat cell size (P<.05) and LPL activity (P<.05) but had no influence on lipid accretion. Quantitative analysis of adipose tissue sections provided direct and indirect evidence of a “critical” or “sensitive” period between 90 and 105 days, since fetal hypox at day 70 severely impeded preadipocyte recruitmentheplication during this period. Furthermore, T₄ but not GH effectively normalized this hypox-induced deficiency in preadipocyte development. Therefore, T₄ may have a major role in preadipocyte recruitmentheplication during late fetal life.     

Methane emissions from two breeds of beef cows offered diets containing barley straw with either grass silage or brewers’ grains

Increasing the concentration of dietary lipid is a promising strategy for reducing methane (CH₄) emissions from ruminants. This study investigated the effect of replacing grass silage with brewers’ grains on CH₄ emissions of pregnant, non-lactating beef cows of two breeds. The experiment was a two×two factorial design comprising two breeds (LIMx, crossbred Limousin; and LUI, purebred Luing) and two diets consisting of (g/kg diet dry matter (DM)) barley straw (687) and grass silage (301, GS), or barley straw (763) and brewers’ grains (226, BG), which were offered ad libitum. Replacing GS with BG increased the acid-hydrolysed ether extract concentration from 21 to 37 g/kg diet DM. Cows (n=48) were group-housed in equal numbers of each breed across two pens and each diet was allocated to one pen. Before measurements of CH₄, individual dry matter intake (DMI), weekly BW and weekly body condition score were measured for a minimum of 3 weeks, following a 4-week period to acclimatise to the diets. CH₄ emissions were subsequently measured on one occasion from each cow using individual respiration chambers. Due to occasional equipment failures, CH₄ measurements were run over 9 weeks giving 10 observations for each breed×treatment combination (total n=40). There were no differences between diets for daily DMI measured in the chambers (9.92 v. 9.86 kg/day for BG and GS, respectively; P>0.05). Cows offered the BG diet produced less daily CH₄ than GS-fed cows (131 v. 156 g/day: P<0.01). When expressed either as g/kg DMI or kJ/MJ gross energy intake (GEI), BG-fed cows produced less CH₄ than GS-fed cows (13.5 v. 16.4 g/kg DMI, P<0.05; 39.2 v. 48.6 kJ/MJ GEI, P<0.01). Breed did not affect daily DMI or CH₄ expressed as g/day, g/kg DMI or kJ/MJ GEI (P>0.05). However, when expressed as a proportion of metabolic BW (BW^0.75), LUI cows had greater DMI than LIMx cows (84.5 v. 75.7 g DMI/kg BW^0.75, P<0.05) and produced more CH₄ per kg BW^0.75 than LIMx cows (1.30 v. 1.05 g CH₄/kg BW^0.75; P<0.01). Molar proportions of acetate were higher (P<0.001) and propionate and butyrate lower (P<0.01) in rumen fluid samples from BG-fed compared with GS-fed cows. This study demonstrated that replacing GS with BG in barley straw-based diets can effectively reduce CH₄ emissions from beef cows, with no suppression of DMI.     

Are dairy cows with a more reactive temperament less efficient in energetic metabolism and do they produce more enteric methane?

It remains unknown whether dairy cows with more reactive temperament produce more enteric methane (CH₄) and are less bioenergetically efficient than the calmer ones. The objectives of this study were (a) to evaluate the relationship between cattle temperament assessed by traditionally used tests with energetic metabolism and enteric CH₄ emissions by crossbred dairy cows; (b) to assess how cows’ restlessness in respiration chambers affects energetic metabolism and enteric CH₄ emissions. Temperament indicators were evaluated for 28 primiparous F1 Holstein-Gyr cows tested singly in the handling corral (entrance time, crush score, flight speed, and flight distance) and during milking (steps, kicks, defecation, rumination, and kick the milking cluster off). Cows’ behaviors within respiration chambers were also recorded for each individual kept singly. Digestibility and calorimetry trials were performed to obtain energy partitioning and CH₄ measures. Cows with more reactive temperament in milking (the ones that kicked the milking cluster off more frequently) spent 25.24% less net energy on lactation (P = 0.04) and emitted 36.77% more enteric CH₄/kg of milk (P = 0.03). Furthermore, cows that showed a higher frequency of rumination at milking parlor allocated 57.93% more net energy for milk production (P < 0.01), spent 50.00% more metabolizable energy for milk production (P < 0.01) and 37.10% less CH₄/kg of milk (P = 0.04). Regarding the handling temperament, most reactive cows according to flight speed, lost 29.16% less energy as urine (P = 0.05) and tended to have 14.30% more enteric CH₄ production (P = 0.08), as well as cows with a lower entrance time (most reactive) that also lost 13.29% more energy as enteric CH₄ (P = 0.04). Temperament and restless behavior of Holstein-Gyr cows were related to metabolic efficiency and enteric CH₄ emissions. Cows’ reactivity and rumination in the milking parlor, in addition to flight speed and entrance time in the squeeze chute during handling in the corral, could be useful measures to predict animals more prone to metabolic inefficiency, which could negatively affect the sustainability of dairy systems.     

Role of maternal tissue in the synthesis of polyunsaturated fatty acids in response to a lipid-deficient diet during pregnancy and lactation in rats

During pregnancy and lactation, metabolic adaptations involve changes in expression of desaturases and elongases (Elovl2 and Elovl5) in the mammary gland and liver for the synthesis of long-chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic acid (AA) required for fetal and postnatal growth. Adipose tissue is a pool of LC-PUFAs. The response of adipose tissue for the synthesis of these fatty acids in a lipid-deficient diet of dams is unknown. The aim of this study was to explore the role of maternal tissue in the synthesis of LC-PUFAs in rats fed a low-lipid diet during pregnancy and lactation. Fatty acid composition (indicative of enzymatic activity) and gene expression of encoding enzymes for fatty acid synthesis were measured in liver, mammary gland and adipose tissue in rats fed a low-lipid diet. Gene expression of desaturases, elongases, fatty acid synthase (Fasn) and their regulator Srebf-1c was increased in the mammary gland, liver and adipose tissue of rats fed a low-lipid diet compared with rats from the adequate-lipid diet group throughout pregnancy and lactation. Genes with the highest (P < 0.05) expression in the mammary gland, liver and adipose tissue were Elovl5 (1333%), Fads2 (490%) and Fasn (6608%), respectively, in a low-lipid diet than in adequate-lipid diet. The percentage of AA in the mammary gland was similar between the low-lipid diet and adequate-lipid diet groups during the second stage of pregnancy and during lactation. The percentage of monounsaturated and saturated fatty acids was significantly (P < 0.05) increased throughout pregnancy and lactation in all tissues in rats fed a low-lipid diet than in rats fed an adequate-lipid diet. Results suggest that maternal metabolic adaptations used to compensate for lipid-deficient diet during pregnancy and lactation include increased expression of genes involved in LC-PUFAs synthesis in a stage- and tissue-specific manner and elevated lipogenic activity (saturated and monounsaturated fatty acid synthesis) of maternal tissues including adipose tissue.     

Effects of Supplementary Selenium Source on the Blood Parameters in Beef Cows and Their Nursing Calves

Over 2 years, 32 beef cows nursing calves in southwest Arkansas were randomly selected from a herd of 120 that were managed in six groups and were assigned to six 5.1-ha bermudagrass (Cynodon dactylon [L.] Pers.) pastures. Treatments were assigned to pastures (two pastures/treatment) and cows had ad libitum access to one of three free-choice minerals: (1) no supplemental selenium (Se), (2) 26 mg of supplemental Se from sodium selenite per kilogram, and (3) 26 mg of supplemental Se from seleno-yeast per kilogram (designed mineral intake?=?113 g/cow daily). Data were analyzed using a mixed model; year and pasture were the random effects and treatment was the fixed effect. At the beginning of the calving and breeding seasons, cows supplemented with Se had greater (P?<?0.01) whole blood Se concentration (WBSe) and glutathione peroxidase activities (GSH-Px) than cows receiving no supplemental Se; cows fed seleno-yeast had greater (P?≤?0.05) WBSe than cows fed sodium selenite, but GSH-Px did not differ (P?≥?0.25) between the two sources. At birth and near peak lactation (late May), calves from cows supplemented with Se had greater (P?<?0.01) WBSe than calves from cows fed no Se and calves from cows fed seleno-yeast had greater (P?≤?0.01) WBSe and GSH-Px than calves from cows fed sodium selenite. Thyroxine (T₄), triiodothyronine (T₃), and the T₄:T₃ ratio in calves did not differ among treatments (P?≥?0.35). At birth, insulin-like growth factor 1 (IGF-1) was greater (P?=?0.02) in calves nursing cows with no supplemental Se than in ones with supplemental Se; in calves nursing cows with supplemental sodium selenite, IGF-1 did not differ (P?=?0.96) from ones offered supplemental seleno-yeast. Selenium supplementation of gestating beef cows benefited cows and calves by increasing WBSe and GSH-Px. The use of seleno-yeast as a Se supplement compared to sodium selenite increased the WBSe of both cows and their calves without affecting the T₄ to T₃ conversion or IGF-1 concentrations.     

Metabolic hormones,grazing behaviour,offspring physical distance and productive response of beef cow grazing at two herbage allowances

Herbage allowance (HA) management during gestation–lactation cycle of cows grazing native grasslands improves pregnancy rates and calves’ weaning weight records. Those improvements were associated with greater herbage mass, and better body condition score (BCS) and metabolic status of the cows, which could affect grazing and maternal behaviour, particularly when temporary suckling restriction (TSR) and flushing (FL) is applied. The objective of this study was to evaluate the effect of HA during the gestation–lactation period on cows’ and calves’ liveweight (LW), BCS, milk yield, insulin, IGF-1 and leptin concentrations, as well as the proportion of diurnal grazing activities (grazing, ruminating, walking and idling), and maternal behaviour from −10 to 70 days relative to TSR (day 0 = initiation of TSR at 86 ± 10 days relative to calving). Thirty-three primiparous Hereford cows were allocated to HA treatments during gestation and lactation, which annually averaged 2.5 (low = LHA) and 4 kg DM/kg LW (high = HHA). The LW and BCS of cows did not differ during −10 to 50 days but were greater in HHA than LHA at the end of the study (P < 0.05). Concentrations of IGF-1 were greater in HHA compared to LHA, while insulin and leptin did not differ. Grazing was lower in HHA than LHA, and the opposite occurred with ruminating and idling (P < 0.05). Cow–calf physical distance was greater in LHA cows compared to HHA (P < 0.05) and increased greatly in the former group after FL, while this increase was lower and later in HHA cows. Milk yield was greater in HHA (P < 0.05), and calves’ weight did not differ between treatments from day −10 to 35, but was greater in HHA compared to LHA from 45 days until the end of the study. Thus, the HHA in a low herbage height and mass condition resulted in greater IGF-1 concentrations and milk yield, and induced changes in grazing and maternal behaviour that were associated with increased cows’ LW, BCS and calves’ weight at the end of the study.     

Effects of progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI in beef cattle

Three experiments were conducted to determine the effects of low-dose progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI (TAI) in beef cattle (GnRH on Day 0, PGF_2α on Day 7, with GnRH and TAI on Day 9, 54-56 h after PGF_2α). Experiments 1 and 2 were 2 × 2 factorials with presynchronization (with or without a once-used CIDR; Days −15 to 0 in Experiment 1 and Days −7 to 0, with PGF_2α at insertion, in Experiment 2), and with or without 400 IU eCG on Day 7 in suckled cows. In Experiment 3, suckled cows and nulliparous heifers were either presynchronized with a twice-used CIDR (Days −5 to 0) and PGF_2α at insertion, or no treatment prior to insertion of a new CIDR (Days 0-7). Presynchronization increased (P < 0.05) ovulation rate to GnRH on Day 0 (75.0% vs 48.7%, 76.7% vs 55.0%, and 60.0% vs 36.1% for Experiments 1, 2, and 3, respectively), increased the diameter of the preovulatory follicle in Experiments 1 and 2, and increased the response to PGF_2α (regardless of parity) in Experiment 1 (P < 0.01), and in primiparous cows in Experiment 2 (P < 0.01). Effects of presynchronization on pregnancy rates (53.4% vs 54.1%, 57.7% vs 45.3%, and 54.3% vs 44.4% for Experiments 1, 2, and 3, respectively) were influenced by parity and eCG (P < 0.05). Treatment with eCG had no effect (P > 0.05) on the diameter of the preovulatory follicle (Experiment 1), or the response to PGF_2α (Experiments 1 and 2), but tended (P = 0.08) to improve pregnancy rates, especially in primiparous cows that were not presynchronized (P < 0.01). However, the effects of eCG and presynchronization were not additive.