Influence of gestation on jugular plasma thyroxine levels in Murrah buffalo and Karan Swiss cows

Plasma samples from 106 pregnant Karan Swiss (Brown Swiss x Sahiwal) cows and 108 Murrah buffalo were tested for thyroxine (T(4)) levels to determine the relationship between the hormonal changes and advancing pregnancy in the two species. All samples were collected within 2 months (January and February) to avoid seasonal interference on T(4) levels. In pregnant cows, the concentration of T(4) increased sharply during the first trimester, reaching a peak at the third month of gestation followed by a gradual decline until the last month of pregnancy. In pregnant buffalo, peripheral plasma T(4) levels fluctuated slightly throughout pregnancy without exhibiting a specific trend. Statistical analysis revealed that the magnitude of T(4) levels was significantly lower in buffalo (P < 0.01) than in the cows throughout pregnancy and that the hormonal patterns of the two species were significantly different (P < 0.05) during gestation. It was hypothesized from this study that T(4) requirements for the fetal buffalo calf may be lower than that for the fetal cattle calf since the buffalo gestation period is a month longer and the metabolic rate lower vis-a-vis the cow.     

Use of bovine pregnancy-associated glycoproteins to predict late embryonic mortality in postpartum Nelore beef cows

The primary objective was to determine if circulating concentration of bovine pregnancy-associated glycoproteins (bPAGs) on Day 30 after artificial insemination (AI) may serve as a marker of late embryonic mortality in Bos indicus (Nelore) beef cows. In experiment 1, postpartum Nelore beef cows (n = 56) were artificially inseminated at a fixed time (Day 0) after synchronization of ovulation. Serum samples were collected on Days 0, 21, 24, 27, and 30 after AI. The first significant increase (P < 0.0001) in serum bPAGs after insemination occurred on Day 24 of gestation. In experiment 2, ovulation was synchronized in postpartum Nelore beef cows (n = 1460) and AI was received at a fixed time. Pregnancy diagnosis and blood sample collection were carried out on Days 28 to 30 after insemination. Cows that maintained a pregnancy from Days 28 to 100 of gestation (n = 714) had significantly (P < 0.0001) higher circulating concentrations of bPAGs on Day 28 compared with cows that did not maintain a pregnancy (embryonic mortality [EM]) until Day 100 (n = 89). When Day 28 bPAG concentration was included in a logistic regression model to predict pregnancy maintenance until Day 100 of gestation, there was an increase (P < 0.0001) in the probability of maintaining pregnancy as maternal concentrations of bPAGs increased. A receiver operating characteristic curve was generated to determine bPAG concentrations on Day 28 that should predict embryonic survival or mortality with an accuracy of 95% or more. On the basis of the positive and negative predicative value analysis, at Day 28 of gestation a circulating concentration of bPAGs greater than 7.9 ng/mL was 95% accurate in predicting embryonic maintenance (to Day 100); a concentration of bPAGs less than 0.72 ng/mL was 95% accurate in predicting EM by Day 100. In experiment 3, the preceding model was tested in a separate set of Nelore beef cows to validate whether bPAGs would serve as an accurate measure of late embryonic mortality. Ovulation was synchronized in 650 Nelore cows and received AI at a fixed time. Pregnancy diagnosis and bPAG sampling were performed at Day 28 of gestation. Only pregnant cows were included in the analysis. On the basis of the previously reported bPAG cutoff values, the test was 95% accurate in predicting late embryonic mortality at Day 28 of gestation. In summary, bPAGs seem to be a good marker for predicting EM between Days 28 and 100 of gestation and suggest that this model could help dissect the molecular mechanisms leading to late EM.     

The effect of calf removal on estrous response and pregnancy rate of beef cows after SYNCRO-MATE-B treatment

The effect of calf removal on estrous response and pregnancy rate of cows given SYNCRO-MATE-B (SMB) was determined. Two hundred forty three lactating beef cows treated with SMB were allotted to three treatments: treatment 1, no calf removal; treatment 2, 24 hr calf removal and treatment 3, 48 hr calf removal. Calf removal time began with removal of the SMB implant. All cows were artificially inseminated 48 to 54 hr after implant removal. Body condition of cows in each heard was visually appraised as adequate or marginal. At each location, technicians and sires were stratified across all treatments.Estrous response of cows (n=143) was different (P<.01) between treatments which averaged 23, 40 and 77 percent for treatments 1, 2 and 3, respectively. Pregnancy rates of cows (n=243) after the first artificial insemination (AI) were 32, 28 and 46 percent for treatments 1, 2 and 3, respectively. The pregnancy rate was greater (P<.05) for treatment 3 than other treatments. After 25 days of breeding, the pregnancy rates were 59, 58 and 72 percent, respectively, for the three treatments. There was a linear relationship between days postpartum at the time of treatment and estrous response (P<.01) and first service pregnancy rate (P<.05). The partial regression coefficients for estrous response and first service pregnancy rate were 1.2 and .6 percent, respectively.In summary, estrous response and pregnancy rate of lactating beef cows treated with SMB were increased by 48 hr calf removal, compared to no calf removal or 24 hr calf removal, when calf removal time began with removal of the SMB implant.     

Influences of diet during gestation on potential postpartum reproductive performance and milk production of beef heifers

The influences of nutritional protein and energy during early and mid pregnancy on milk production and postpartum reproductive parameters were determined in 70 beef heifers of two composite breeds (Bos indicus X Bos taurus). At artificial insemination (AI), heifers were divided into four dietary treatment groups identified by the level of protein, and to a lesser extent energy, fed during the first and second trimesters: high/high (HH), high/low (HL), low/high (LH), and low/low (LL). Milk production was lower in the heifers receiving high treatment in first trimester than that in heifers receiving the low treatment (P = 0.01). Milk production was negatively associated with dam body condition score (BCS; P = 0.01), nonesterified fatty acids (P = 0.001), and leptin (P = 0.02) and positively associated with urea (P < 0.001) concentrations during lactation. Increased dietary protein in the first trimester increased or decreased concentrations of colostral protein dependent upon genotype (P = 0.03). Colostral protein was positively associated with bovine pregnancy associated glycoprotein from late gestation (P = 0.007). Milk fat was negatively associated with BCS (P = 0.007) and influenced by genotype (P = 0.003). Dietary treatment did not affect the postpartum reproductive performance of beef heifers. Gestation length (P < 0.001) and the postpartum interval to first estrus (PPI; P = 0.02) were positively associated with calf size. Placental size was negatively associated with placental expulsion time (P < 0.01). Prepartum BCS of the heifers was negatively associated with PPI (P = 0.01). Overall, high levels of nutrition during early gestation are detrimental to milk production in beef heifers.     

Detection of pregnancy by radioimmunoassay of a novel pregnancy-specific protein in serum of cows and a profile of serum concentrations during gestation

The development of a double antibody radioimmunoassay for a bovine pregnancy-specific protein (pregnancy-specific protein B; PSPB) is presented. By means of this assay, PSPB could be measured in serum of pregnant cows. Five dairy cows were bled throughout gestation to measure serum levels of PSPB. Serum concentrations (means +/- SE) exceeded 1 ng/ml by 30 days postbreeding and increased gradually through three months (9 +/- 0.6 ng/ml), six months (35 +/- 6 ng/ml), and nine months (150 +/- 75 ng/ml) of gestation. Maximum levels of PSPB (542 +/- 144 ng/ml) were reached two days before parturition and then steadily declined to less than 78 ng/ml by 21 days postpartum. In 21 cows bled daily from 15 through 30 days postbreeding, PSPB could be measured in a few cows before and in most cows by 24 days after breeding. In a commercial herd of 102 beef cows, the assay could detect pregnancy earlier and more accurately than the routine method of rectal palpation. This radioimmunoassay measures a unique antigen that, for the first time, provides a serological method for detecting pregnancy in cows.     

Effect of a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.     

Impacts of protein supplementation during late gestation of beef cows on maternal skeletal muscle and liver tissues metabolism

Since nutritional requirements are increased at the end of gestation to meet the demands of the pregnant uterus, pregnant beef cows are susceptible to mobilization of body reserves (mainly fat and amino acids (AAs)) and to alter the metabolism of nutrients in the liver and muscle to support such demands. The objective of this study was to evaluate the effect of CP supplementation on maternal nutrient metabolism in the late gestation of beef cows grazing a low-quality pasture. Forty-three pregnant Nellore cows gestating male fetuses (average age = 6 years; average weight = 544 kg) at 193 ± 30 (mean ± SD) days (d) of gestation were divided into eight groups (experimental units, with four to five cows each). Treatments were (1) control (CON, n = 4): pasture-based (PB) diet without CP supplementation and (2) supplemented (SUP, n = 4): PB diet daily supplemented with 2 g/kg of BW of a 43.5% CP supplement. Liver and skeletal muscle biopsies were performed at 265 days of gestation and samples were collected for mRNA expression. On day 280 of gestation, blood samples were collected to assess plasma levels of AA. The CON-fed cows tended to have greater (P = 0.057) total circulating AA than SUP-fed cows. The circulating glycogenic AA was greater (P = 0.035) in CON than in SUP cows. CON cows was greater for histidine (P = 0.015), methionine (P = 0.007) and alanine (P = 0.036) than SUP cows. The CON- and SUP-fed showed no differences for gluconeogenesis, fatty acid transport and signaling axis markers in the liver. The mRNA expression of markers for skeletal muscle synthesis, p7056k (P = 0.060) and GSK3B (P = 0.096), tended to be greater in cows from CON than SUP group. No differences were found for mRNA expression of markers for skeletal muscle degradation. We conclude that CP supplementation to CP-restricted late-pregnant beef cows reduces the maternal tissue mobilization and changes the profile of plasma circulating AA and the mRNA expression of markers for the synthesis of skeletal muscle tissue.     

Using animal-mounted sensor technology and machine learning to predict time-to-calving in beef and dairy cows

Worldwide, there is a trend towards increased herd sizes, and the animal-to-stockman ratio is increasing within the beef and dairy sectors; thus, the time available to monitoring individual animals is reducing. The behaviour of cows is known to change in the hours prior to parturition, for example, less time ruminating and eating and increased activity level and tail-raise events. These behaviours can be monitored non-invasively using animal-mounted sensors. Thus, behavioural traits are ideal variables for the prediction of calving. This study explored the potential of two sensor technologies for their capabilities in predicting when calf expulsion should be expected. Two trials were conducted at separate locations: (i) beef cows (n = 144) and (ii) dairy cows (n = 110). Two sensors were deployed on each cow: (1) Afimilk Silent Herdsman (SHM) collars monitoring time spent ruminating (RUM), eating (EAT) and the relative activity level (ACT) of the cow, and (2) tail-mounted Axivity accelerometers to detect tail-raise events (TAIL). The exact time the calf was expelled from the cow was determined by viewing closed-circuit television camera footage. Machine learning random forest algorithms were developed to predict when calf expulsion should be expected using single-sensor variables and by integrating multiple-sensor data-streams. The performance of the models was tested using the Matthew’s correlation coefficient (MCC), the area under the curve, and the sensitivity and specificity of predictions. The TAIL model was slightly better at predicting calving within a 5-h window for beef cows (MCC = 0.31) than for dairy cows (MCC = 0.29). The TAIL + RUM + EAT models were equally as good at predicting calving within a 5-h window for beef and dairy cows (MCC = 0.32 for both models). Combining data-streams from SHM and tail sensors did not substantially improve model performance over tail sensors alone; therefore, hour-by-hour algorithms for the prediction of time of calf expulsion were developed using tail sensor data. Optimal classification occurred at 2 h prior to calving for both beef (MCC = 0.29) and dairy cows (MCC = 0.25). This study showed that tail sensors alone are adequate for the prediction of parturition and that the optimal time for prediction is 2 h before expulsion of the calf.     

Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate, 48-hour calf removal and PGF2alpha

One hundred and sixty-five suckled postpartum beef cows were utilized to evaluate the effectiveness of 2 estrus synchronization systems for the initiation and synchronization of estrus. The treatment groups consisted of 1) melengestrol acetate (MGA)-PGF2alpha (cows were given 0.5 mg MGA/head/day for 14 d with 25 mg PGF2alpha injected 17 d after the last day of MGA administration); 2) MGA-48-h calf removal (CR)-PGF2alpha (cows were given 0.5 mg MGA/head/day for 14 d with 48-h calf removal starting on the second day after completion of the MGA regimen plus 25 mg PGF2alpha administered 17 d after the last day of MGA); and 3) unsynchronized controls. Cows were assigned to treatments by the numbers of days post partum, body condition, age, and breed of sire. The cows were observed for estrus at 12-h intervals for 5 d after PGF2alpha administration and were artificially inseminated 12 to 18 h after the observed estrus. Both the MGA-PGF2alpha and MGA-CR-PGF2alpha treatments (64.8 and 61.8%) had greater (P < 0.05) 5-d estrus rates than the control treatments (34.5%). The synchronized pregnancy rate was greater (P < 0.05) for the MGA-CR-PGF2alpha than the control treatment.(52.7 vs 30.9%, respectively). The MGA-CR-PGF2alpha cows had a higher 25-d pregnancy rate than either the MGA-PGF2alpha (P < 0.05) or control cows (P < 0.08). Of the anestrous cows at the beginning of treatment, more MGA-CR-PGF2alpha (P = 0.1) and MGA-PGF2alpha cows were cyclic posttreatment than control cows (58.7 and 55.1 vs 44.7%, respectively), suggesting that treatment initiated estrous cycles in only a small number of the anestrous cows. Both MGA-PGF2alpha and MGA-CR-PGF2alpha treatments appear to be effective methods of synchronizing estrus in suckled postpartum beef cows. However, MGA-CR-PGF2alpha was more effective in establishing pregnancy earlier in the breeding season than MGA-PGF2alpha.     

Short- and long-term effects of temporary early cow–calf separation or restricted suckling on well-being and performance in zebu cattle

Information on weaning techniques in the tropics is scarce, particularly regarding the long-term effect of temporary early cow–calf separation or restricted suckling. Therefore, we studied the effects of these two handling practices on well-being and performance at 150 days postpartum in fifteen zebu cow–calf pairs randomly assigned to three treatments. Continuous suckling (CS) where calves remained with their dams from birth to weaning; restricted suckling (RS) calves were allowed to suckle 30 min/day from Day 34 until weaning at Day 150 and kept separated the rest of the time; temporary separation (TS) calves were separated for 72 h from their dams from Day 33 to 36 but remained with their dams the rest of the time. Blood samples and behavioral data were collected on Days 32–36 (1st period) and 149–153 (2nd period). In the 1st period, a greater percentage of RS and TS calves were observed close to the fence line (< 10 m) that separated them from their dams (P < 0.0001) and vocalized more than CS calves (P < 0.0001), while in the 2nd period, RS calves had the highest cortisol concentration and vocalization rate (P < 0.05). Similarly, during the 1st period, a greater percentage of RS and TS cows were observed close to the fence line than CS cows (P < 0.0001), with TS cows vocalizing the most (P = 0.001). In the 2nd period, RS cows had greater cortisol concentration than TS (P = 0.037) and CS cows (P = 0.003). More TS and CS cows than RS were observed close to the fence line (P = 0.03 and P = 0.05). On Day 150, TS calves and cows vocalized more than RS and CS animals (P < 0.0001). Before calf–cow separation, 27 out of 45 cows were cycling (CS = 10; RS = 6; TS = 11). After separation, 12 of the remaining 18 cows resumed ovarian activity (CS = 3; RS = 5; TS = 4), and all cows were cycling after estrous synchronization treatment. The pregnancy rate was similar between CS, RS, and TS (60, 53, and 60% respectively). In conclusion, temporary separation increased calf distress response to definitive weaning even four months later, while restricted suckling seemed to reduce it.     

Reproductive function in beef cows calving in the spring or fall

Plasma progesterone was determined twice weekly for approximately 100 days postpartum in suckled purebred (Hereford) and crossbred (beef x dairy) cows that calved in the spring or late summer/fall season. The progestèrone profiles and occurrence of estrus were used to determine ovulation times and to monitor ovarian function. Postpartum ovulations occurred significantly earlier in crossbred than in purebred cows (38.1 ± 18.5 vs. 58.1 ± 21.8, P<0.01) and in fall compared to spring calving cows (32 ± 13.9 vs. 59.1 ± 20.3, P<0.001). Rations providing either 70 or 100% of requirements for metabolizable energy were fed from 30 days prepartum until the end of the subsequent rebreeding period. Cows receiving the 70% energy ration ovulated slightly earlier but there was no effect of ration on days to pregnancy. The minimal effect of energy ration was not unexpected in this trial since many of the cows were overconditioned during late gestation.The correlation between calendar date of calving and interval to first ovulation was significant for spring (r = ?0.38, P<0.01) but not for fall calving animals. Since cows were confined and received a balanced ration of stored feeds throughout the year, photoperiod and/or temperature rather than nutritional factors would be the probable cause of delayed ovarian activity in spring calvers.Reproductive performance was assessed during the period when samples were collected and the response for purebred (n=105) and crossbreds (n=142), respectively were: ovulated by day 60 postpartum, 57 vs. 87%; mated by day 100 without conception, 17 vs. 26%; ovulated before day 100 without detection and mating, 10 vs. 4%; anovulatory to day 100, 7 vs. 0%; pregnant by day 100, 67 vs. 70%. Similar comparisons for spring (n=133) and summer/fall (n=144) calvers, respectively, were: ovulated by 60 days postpartum, 56 vs. 96%; mated by day 100 without conception, 27 vs. 17%; ovulated by day 100 without detection and mating, 8 vs. 5%; anovulatory to day 100, 5 vs. 0%; pregnant by day 100, 60 vs. 78%. The difference with the greatest practical significance is that a higher proportion of the late summer/fall calving animals were pregnant by day 100 postpartum (P<0.01) which indicates that reproductive performance is superior in fall calving beef cows.     

Genome-wide association study of economically important traits in Charolais and Limousin beef cows

Genomic selection has proven effective for advancing genetic gain for key profit traits in dairy cattle production systems. However, its impact to-date on genetic improvement programs for beef cattle has been less effective. Despite this, the technology is thought to be particularly useful for low heritability traits such as those associated with reproductive efficiency. The objective of this study was to identify genetic variants associated with key determinants of reproductive and overall productive efficiency in beef cows. The analysis employed a large dataset derived from the national genetic evaluation program in Ireland for two of the most predominant beef breeds, viz. Charolais (n = 5 244 cows) and Limousin (n = 7 304 cows). Single nucleotide polymorphisms (SNPs) were identified as being statistically significantly associated (adj. P < 0.05) with both reproductive and productive traits for both breed types. However, there was little across breed commonality, with only two SNPs (rs110240246 and rs110344317; adj. P < 0.05) located within the genomic regions of the LCORL and MSTN genes respectively, identified in both Charolais and Limousin populations, associated with traits including carcass weight, cull-cow weight and live-weight. Significant SNPs within the MSTN gene were also associated with both reproduction and production related traits within each breed. Finally, traits including calving difficulty, calf mortality and calving interval were associated with SNPs within genomic regions comprising genes involved in cellular growth and lipid metabolism. Genetic variants identified as associated with both important reproductive efficiency and production related traits from this study warrant further analyses for their potential incorporation into breeding programmes to support the sustainability of beef cattle production.     

Relationships between calf birth weight, prepartum concentrations of plasma energy metabolites and resumption of ovulation postpartum in Limousine suckled beef cows

The aim of this study was to determine the relationship between energy status before calving and calf birth weight and their potential effects on interval between calving and first ovulation. Sixty-nine Limousine, suckled beef cows were sampled weekly over a 3-yr period during the last 2 m.o. of pregnancy to determine the concentrations of nonesterified fatty acids (NEFA), beta-3-hydroxybutyrate (beta-OHB), glucose and glycerol. After parturition, progesterone concentrations were measured weekly to determine time of resumption of ovulation. Cows were allotted to 3 groups according to calf birth weight (Heavy: > 44 kg, n = 37; Medium: 39 to 43 kg, n = 56; and Light: < 38 kg, n = 45) and to postpartum ovarian resumption of cyclicity (Late: > 11 wk, n = 41; Mid: 7 to 10 wk, n = 57; and Early: < 6 wk, n = 40). Puerperium glycaemia of the dams was steady state (0.66 +/- 0.03 g/L) and was not related to calf birth weight. Plasma NEFA, beta-OHB and glycerol values were higher (P < 0.05) in Heavy than in Medium and Light group dams during the last 4 wk of pregnancy. Interval between calving and first ovulation was significantly longer for primiparous than for multiparous cows (respectively, 9.9 +/- 2.0 and 7.7 +/- 1.4 wk; P < 0.05). Calf birth weight was not related to time of first ovulation. Late primiparous cows had higher NEFA plasma concentrations than Mid and Early group primiparous cows during the last 4 wk of pregnancy, whereas NEFA plasma concentrations were not related to interval between calving and first ovulation in multiparous cows. Thus, lipomobilization increased with calf birth weight during the last 4 wk of pregnancy. High level of body reserves mobilization was associated with delayed first ovulation in primiparous but not in multiparous cows.     

Dynamics of heat shock protein 70 concentrations in peripheral blood lymphocyte lysates during pregnancy in lactating Holstein-Friesian cows

The aim of this study was to characterize the dynamics of the concentrations of heat shock protein 70 kDa (HSP70) in peripheral blood lymphocytes of lactating Holstein-Friesian dairy cows (Bos taurus) during pregnancy. The detection of pregnancy was carried out and blood samples collected on Days 40, 90, 120, 150, 180, and 210 of gestation from 46 cows (11 primiparous and 35 pluriparous, 34 seropositive and 12 seronegative to Neospora caninum). Peripheral blood lymphocytes were isolated by density gradient centrifugation. Serologic analysis of Neospora infection and determinations of HSP70 concentrations in lymphocyte lysates were carried out using commercial enzyme-linked immunosorbent assay kits. Climate variables were monitored using on-farm data loggers. Heat shock protein 70 concentrations increased in lymphocytes as gestation progressed, particularly in primiparous cows, with no effect from Neospora infection, climate variables, milk production, semen-providing bull, or outcome of gestation (singletons or twins). Our results show that HSP70 concentrations increased in lymphocytes as gestation progressed and were not affected by stressful factors, such as milk production, heat stress, chronic infection (neosporosis), or twin pregnancies.     

Postpartum fertility in beef cattle producing twins

Postpartum fertility was measured in 42 plur iparous Hereford cows and first calf Hereford heifers that calved after embryo transfer to induce twins. Dams were exposed to a Hereford bull from 4: 00 P.M. to 8:00 A.M. each day from 60 days postpartum until pregnancy was confirmed or calves were weaned at 180 days of age. Days open ($\text{X}\text{± SE}$) for dams that produced single and twin calves were 84.1 ± 4.6 (n = 12) and 94.9 ± 6.2 (n = 30), respectively. Corresponding values for dams that nursed one calf, including six females that lost one calf of a twin set at birth, and dams that nursed twins were 89.3 ± 6.4 (n = 18) and 93.4 ± 8.5 (n = 24). No significant differences were observed due to calving or suckling twin calves. Heifers that calved twins had a shorter mean interval to conception than cows that calved twins. These results are interpreted to mean that with proper management during the prepartum and postpartum periods, reduced fertility in beef cattle that produce twins need not occur.     

Inferences of body energy reserves on conception rate of suckled Zebu beef cows subjected to timed artificial insemination followed by natural mating

The influence of body condition score (BCS), rump fat thickness (RFAT), and live weight (LW), and the changes in these parameters during the interval from 165 of prepartum (i.e., 125 days of prior gestation) to 112 postpartum on first service conception and pregnancy rates were investigated in suckled Zebu (Bos indicus) beef cows (n = 266) subjected to timed artificial insemination (TAI) followed by natural mating. The aforementioned parameters were recorded at 165 ± 14 days (mean ± standard error) prepartum (concurrent with the weaning of previous calf), at parturition, and at 42 ± 7 days (at the onset of the synchronization of ovulation protocol), 82 ± 7 days (30 days after TAI), and 112 ± 7 days (60 days after TAI) postpartum. At the start of the breeding season (BS), cows were subjected to a synchronization of ovulation program for TAI. Bulls were placed with cows 10 days after TAI and remained until the end of the study (112 days postpartum). Cows with the highest BCS at parturition had an increased probability of first service conception rate at 60 days after TAI (P = 0.02) and a reduced probability of occurrence of pregnancy loss (P = 0.05). Also, cows had a greater likelihood of conceiving postpartum if they had greater RFAT and BCS at 165 ± 14 days prepartum (P = 0.01 and P = 0.03, respectively) and at parturition (P = 0.0007 and P = 0.003, respectively). Cows that had an increase in RFAT and BCS during the dry period (i.e., interval from weaning of the previous calf to parturition) also had a greater likelihood of conceiving (P = 0.03 and P = 0.06, respectively) during the BS. Among the different time points, RFAT and BCS at parturition had the largest impact on risk of conception during the BS. The LW was a poor predictor of conception during the BS (P = 0.11–0.68) except for LW at 165 ± 14 days prepartum (P = 0.01). Collectively, the findings indicated that the likelihood of conception during the BS was highest in cows that had an improvement in RFAT and BCS during the dry period. Therefore, assuring a good nutritional status in the dry period (BCS ≥ 3.0 at 165 ± 14 days prepartum and ≥3.25 at parturition) is an important aim to optimize the postpartum conception rate of suckled Zebu beef cows subjected to TAI followed by natural mating.     

Effects of suckling frequency and breed on productive performance,follicular dynamics and postpartum interval in beef cows

One experiment was conducted to determine the influence of suckling frequency (restricted suckling (RS) versus ad libitum suckling (AS)) and breed (Brown Swiss versus Pirenaica) on productive performance, follicular dynamics and postpartum cyclicity resumption in beef cows. Twenty-four spring-calving cows (12 Brown Swiss and 12 Pirenaica) were used. After calving cows were assigned, within breed, to the two suckling frequencies (RS versus AS). During the postpartum period, cows were fed 100% of the daily energy estimated requirements. The study was conducted from calving to either day 90 postpartum or to detection of the second ovulation whenever it came later. The pattern of follicular development was monitored daily by transrectal ultrasonography, and blood samples were collected three times a week to analyse progesterone concentrations by RIA. Body condition score at calving was 2.5 (from 1 to 5). Productive parameters were not significantly affected by suckling frequency. Pirenaica cows gained more weight (P<0.001), while Brown Swiss cows had higher milk yield (P<0.001) and thus their calves grew faster (P<0.05). In the present moderate conditions of nutrition, either suckling frequency or breed did not affect follicular dynamics (on average there were 6.5 follicles in emergence, growth rate of dominant follicle (DF) was 1.3mm per day and maximum diameter of dominant follicle was 13.9mm). There were gradual increases in maximum diameter and growth rate of dominant follicle related to the proximity of the ovulatory waves, and they were defined by third order polynomial equations. Postpartum anoestrous interval (PPI) was markedly affected by the interaction between suckling frequency and breed (P<0.001): ad libitum suckling prolonged significantly the interval from calving to first ovulation in Brown Swiss cows (31.8 day versus 82.7 day, in RS and AS groups, respectively, P<0.05), but not in Pirenaica cows (43.5 day versus 32.6 day, in RS and AS groups, respectively, not statistically significant). It is concluded that in moderate pre- and postpartum nutritional conditions Brown Swiss cows were more susceptible to the suppressor effect of ad libitum suckling on postpartum anoestrous interval than Pirenaica cows, although this breed difference did not seem to be mediated by differences in energy balance or in ovarian follicular dynamics.     

Evaluation of production efficiencies at pasture of lactating suckler cows of diverse genetic merit and replacement strategy

Feed costs account for the largest proportion of direct cost within suckler beef production systems. By identifying the cow type with enhanced capability of converting grazed herbage to beef output across lactations, suckler cow systems would become more efficient and sustainable. The objective of this study was to estimate grass DM intake (GDMI) and production efficiency among lactating suckler cows of diverse genetic merit for the national Irish maternal index (Replacement Index) which includes cow efficiency components such as milk yield and feed intake. Data from 131 cows of diverse genetic merit within the Replacement Index, across two different replacement strategies (suckler or dairy sourced), were available over two grazing seasons. Milk yield, GDMI, cow live weight (BW) and body condition score (BCS) were recorded during early, mid and late-lactation, with subsequent measures of production efficiency extrapolated. Genetic merit had no significant effect on any variables investigated, with the exception of low genetic merit (LOW) cows being 22 kg heavier in BW than high genetic merit (HIGH) cows (P < 0.05). Beef cows were 55 kg heavier in BW (P < 0.001), had a 0.31 greater BCS (P < 0.05) and 0.30 Unité Fourragère Lait (UFL) greater energy requirement for maintenance compared to dairy sourced beef × dairy crossbred (BDX) cows (P < 0.001). The BDX had 0.8 kg greater GDMI, produced 1.8 kg more milk (P < 0.001), had a 0.8 UFL greater energy requirement for lactation and produced weanlings that were 17 kg heavier in BW than beef cows (P < 0.05). Subsequent efficiency variables of milk per 100 kg BW (P < 0.001), milk per kg GDMI (P < 0.001) and GDMI per 100 kg BW (P < 0.001) were more favourable for BDX. The correlations examined showed GDMI had moderate positive correlations (P < 0.001) with intake per 100 kg BW, net energy intake per kg milk yield, RFI and intake per 100 kg calf weaning weight but was weakly negatively correlated to milk yield per kg GDMI (P < 0.001). No difference was observed across genetic merit for beef cows for any of the traits investigated. Results from the current study showed that, while contrasting replacement strategies had an effect on GDMI and production efficiency, no main effect was observed on cows diverse in genetic merit for Replacement Index. Nonetheless, utilising genetic indexes in the suckler herd is an important resource for selecting breeding females for the national herd and phenotypic performance generated from this study can be included in future genetic evaluations to improve reliability of genetic values.