205-d Weight Research Articles

357 The Influence of Supplemental Protein Levels on Beef Cattle Grazing Winter Foothill Rangelands: Cow and Subsequent Calf Performance

Abstract Angus based bred cows [n = 150; initial shrunk body weight (BW) = 615 ± 6.61 kg; initial body condition score (BCS) = 5.2] were used in an 84-d winter grazing experiment that took place over two consecutive years. Cattle were stratified by age and body condition and, within stratum, randomly assigned to one of three protein supplementation treatments: 1) no supplement, 2) cows fed 0.20% BW· d-1 of a 30% protein supplement, and 3) cows fed 0.40% BW · d-1 of a 30% protein supplement. Protein supplement was a 30% CP canola-based pelleted supplement with 9 units protein from urea. Cows were gathered three-times weekly and provided supplement on a replicated pen basis. Performance data were analyzed as a completely randomized design with linear and quadratic contrasts used for mean separation (reps = 5; n = 7). Body weights and BCS were recorded every 28-d period throughout the study and calf BW were obtained at birth and weaning. A treatment × period interaction was detected for body weight change (P < 0.01) where a linear response (P < 0.01) where increasing protein status resulted in modest weight gains relative to the control treatment. BCS also exhibited a linear response for two of the three weight periods (P < 0.01) where level of BCS lost was least in cows with the higher supplemental protein levels. A year × period interaction was detected where cows from year two exhibited less BW change on days 28, 56, and 84 of the study (P < 0.01) and had greater BCS (P < 0.01) than those from year one during these periods. In addition, we observed a treatment × year interaction where cows from year two experienced less BW change and had greater BCS than cows from year one (P < 0.01). No treatment × year interactions were detected for birth weight, average daily gain (ADG), or adjusted 205-d weight in calves. A tendency was noted for cows offered 0.4% BW· d-1 supplement to have heavier calves at birth than their counterparts (P = 0.09) over both years. A year effect was detected where calves born in year two had increased ADG and adjusted 205-d weights compared with those from year one. A tendency (P = 0.09) for the calves in year two of the study to have heavier weights at birth compared with those from year one was also noted. In summary, increasing levels of supplemental protein resulted in linear improvements of BW and BCS of grazing beef cattle during the winter. While birth weights of calves tended to differ due to the gestational nutrition of the dam, calf growth and weaning weights were not affected.

PSIII-8 Late-Breaking: Effect of Feed Additives in Protein Supplements on Reproductive Performance in Young Postpartum Range Cows

Abstract Optimizing reproductive efficiency is crucial in sustaining a successful cattle operation. However, optimizing reproductive performance in young range beef cows is often not captured due to an inability to meet the increased physiological demands. The objective of this study was to determine the impact of feed additives on reproductive performance, cow body weight (BW), body condition score (BCS), and calf growth in young, range beef cows. Data were collected from 2- and 3-year-old range cows (n = 189) from the March-calving herd at the University of Nebraska Gudmundsen Sandhills Laboratory (GSL) located near Whitman, NE over a three-year period (2019-2021). Cows were individually supplemented 908 g/d with one of two 30% crude protein supplement treatments with the addition of either: 1) 160 mg·cow-1·d-1 of rumensin (MON; Elanco Animal Health) or 2) 40 g·cow-1·d-1 of propionate salt (CAP; NutroCal 100; Kemin Animal Nutrition and Health). Supplementation was initiated approximately 7 d after calving and continued for an average of 70 d. Cow BW and BCS were collected weekly from calving to the start of breeding and then again at weaning. On approximately d 60 postpartum, milk production was measured by a modified weigh-suckle-weight technique. Cows were exposed to fertile bulls for a 45-d breeding season starting in June of each year. Cow BW (P ≥ 0.19) and BCS (P ≥ 0.11) were not affected by postpartum supplementation during the study. However, cows receiving CAP did lose more BW (P = 0.04; -7 vs -2 kg for CAP and MON; respectively) from calving to breeding than their counterpart. Calf BW at birth, weaning, or 205-d weight were not impacted (P ≥ 0.68) by the postpartum supplementation strategy. Twenty-four-hour milk production and milk components (fat, solids-non-fat, urea nitrogen) were not influenced (P > 0.21) by postpartum supplementation strategy. However, cows receiving CAP supplement had an increase (P = 0.04; 5.40 vs 5.31% for CAP and MON; respectively) in milk lactose percentage and tended (P = 0.06; 2.56 vs 2.68% for CAP and MON; respectively) to have lower milk protein percentage than their counterpart. Cows receiving CAP supplementation had an increase (P = 0.04; 89 vs 80% for CAP and MON; respectively) in overall pregnancy rate. This study implies that young postpartum cows fed additional glucogenic precursors in the form of propionate salts may increase reproductive efficiency without impacting a change in body weight or body condition score.

Influence of Heifer Post-Weaning Voluntary Feed Intake Classification on Lifetime Productivity in Black Angus Beef Females.

Simple SummaryReplacement beef heifers represent the future of a herd for many cow-calf producers. Producers must invest significant resources into the development of these females as well as consider their maintenance and production costs as mature cows. As a result, selection focuses on replacement heifers that are more efficient in limited nutrition forage base systems. Producers can improve lifetime productivity by ensuring their replacements are of an ideal age and size to be bred as a 2-yr old. Selection criteria may include reproductive ability and breeding history, milk production, and weaning/yearling weights. The ability to select replacement females that are more efficient without negatively affecting overall productivity will help to decreased inputs and alleviate the need for additional expenses such as supplemental feed resources. This study evaluated heifer post-weaning voluntary feed intake (g/kg BW) classification on performance and reproductive measures, as well as impacts on lifetime productivity of 519 commercial Angus beef females. Heifer post-weaning voluntary feed intake (g/kg BW) was calculated over 80 test days following weaning using GrowSafe units. Heifers were categorized based on voluntary feed intake (g/kg BW) as either low (<−0.50 SD from the mean), average (±0.50 SD from the mean), or high (>0.50 SD from the mean) within year. Cow body weight (BW) and body condition score (BCS) at breeding displayed an age effect (p < 0.001), with 2- and 3-year-old cows having lighter BW and lower BCS than 4-yr-old and older cows. Cow BW at weaning showed significance for age and intake (p < 0.001) with younger cows being lighter than older cows, while low intake classified females had greater BW at weaning compared to average and high intake females. Additionally, calf 205-d weights and calf weaning weights (p < 0.01) were significant for age with calves born from older cows weighing more than younger cows. Weaning weight ratio displayed a linear increase with increasing intake classification (p < 0.01). Heifer yearling BW was significant for intake (p < 0.01) with low and average intake heifer classifications having greater heifer yearling BW than cows that had high intake classification as a heifer. Age and intake classification did not impact (p ≥ 0.22) pregnancy status or AI conception. In summary, heifer post-weaning feed intake classification had only minor impacts compared to age effects on lifetime productivity of Angus beef females.

PSII-19 Supplementing Calcium Beta-Hydroxy-Beta-Methylbutyrate (CAHMB) and Vitamin D3 to Sows Increases Piglet Weights

Abstract Previous studies have shown that supplementing sows with calcium beta-hydroxy-beta-methylbutyrate (CaHMB) or CaHMB plus Vitamin D3 in late gestation and/or lactation improved piglet weight through weaning. This study was conducted at a commercial farrowing operation to confirm previous results, and 52 sows were studied, 26 in each of 2 groups. Sows were randomized to receive either 3 g/d CaHMB plus 500 IU/d Vitamin D3 (HMB/D) or a calcium carbonate containing control top-dressed to the morning ration from day 104 of gestation through weaning. Group 1 consisted of older sows, 4th and 5th parity, while Group 2 sows were younger, 2nd and 3rd parity. Three sows failed to farrow, 1 died after farrowing and 1 farrowed late, therefore forty-seven sows were included in the analysis. Treatment with HMB/D had no effect on sow weights, lactational weight loss, pre- or post-farrowing body condition score, stillborn piglets, mummified piglets, or number of piglets born alive or weaned. In both farrowing groups, birth and 24-hour weights of the piglets from HMB/D-supplemented sows were increased (P &amp;lt; 0.0001). Piglets from sows supplemented with HMB/D were 9.7% heavier at birth and at 24 hours were 9.2% heavier, 1,418.6±21.2 and 1,549.3±22.0 g in Control and HMB/D, respectively. Analysis of birth to weaning dates demonstrated that Control piglets were on average one-half day older than HMB/D piglets at weaning (P &amp;lt; 0.0001). However, adjusting the weaning weights to a standardized 21-d weight (5,205.6±99.5 and 5,423.9±103.5 g for Control and HMB/D piglets, respectively) did not demonstrate statistical significance (P = 0.13). Further analysis by group showed HMB/D tended to increase weaning weights in younger sows (Group 2), 5,073.7±142.7 in Controls, 5,431.7±150.7 g in HMB/D piglets (P &amp;lt; 0.09). In conclusion, our results agree with previous studies demonstrating CaHMB and HMB/D supplementation increased early piglet weights with a tendency to improve weaning weights.

Differential response from selection for high calving ease vs. low birth weight in American Simmental beef cattle.

Data on calving ease (CE) and birth, weaning weight (WW), and yearling weight (YW) were obtained from the American Simmental Association (ASA) and included pedigree and performance information on 11,640,735 animals. Our objective was to quantify differential response from selection for high CE vs. low birth weight (LBW) in first-calf Simmental heifers. We hypothesized that direct selection for CE should be used as the primary approach to reduce dystocia and mitigate losses in growth-related traits. WW and YW were adjusted to 205 and 365 d of age, respectively. Sire and maternal grandsire (co)variance components for CE, birth weight (BW), and 205-d weaning weight (205-d WW), and sire covariance components for 160-d postweaning gain (160-d gain) were estimated using a sire-maternal grandsire model. Direct and maternal expected progeny differences (EPD) for CE, BW, and 205-d WW and direct EPD for 160-d gain and 365-d yearling weight (365-d YW) for first-calf Simmental heifers population (465,710 animals) were estimated using a threshold-linear multivariate maternal animal model. This population was used to estimate genetic trends and as a selection pool (control) for various selection scenarios. Selection scenarios were high CE (HCE), LBW, the all-purpose selection index (API = -1.8 BW + 1.3 CE + 0.10 WW + 0.20 YW) of the ASA and its two derived subindices: (API1 = 1.3 CE + 0.20 YW) and (API2 = -1.8 BW + 0.20 YW), and lastly Dickerson's selection index (DSI = -3.2 BW + YW). Data for each selection scenario were created by selecting sires with EPD greater than or equal to the average along with the top 75% of dams. Comparison between selection scenarios involved evaluating the direct and maternal genetic trends from these scenarios. Direct heritabilities for CE, BW, 205-d WW, 160-d gain, and 365-d YW of Simmental cattle were 0.23, 0.52, 0.28, 0.21, and 0.33, respectively. The single trait, HCE, selection scenario, as opposed to LBW, increased the intercept for CE by 57.7% and the slopes (P < 0.001) for BW, 205-d WW, 160-d gain, and 365-d YW by 27.9%, 37.5%, 16%, and 28%, respectively. Comparisons of various selection scenarios revealed that the CE-based selection scenarios (HCE, API, and API1) had a greater response for CE and growth traits.

Genetic and phenotypic associations of feed efficiency with growth and carcass traits in Australian Angus cattle.

Genetic and phenotypic parameters for feed efficiency, growth, and carcass traits for Australian Angus beef cattle were estimated. Growth traits included birth weight (BWT), 200-d weight (200dWT), 400-d weight (400dWT), and 600-d weight (600dWT). Traits associated with feed efficiency were average daily weight gain (ADG), metabolic midweight, average of daily feed intake (FI), feed conversion ratio (FCR), residual feed intake (RFI), and residual gain (RG). Carcass traits involved were carcass eye muscle area (CEMA), carcass intramuscular fat (IMF), subcutaneous fat depths at the 12th/13th rib (CRIB), rump P8 fat depth (P8FAT), and carcass weight (CWT). For growth traits, heritability estimates ranged from 0.14 ± 0.03 for 200dWT to 0.48 ± 0.06 for 600dWT. For feed efficiency traits, direct heritability estimates for FI, FCR, RFI, and RG were 0.55 ± 0.08, 0.20 ± 0.06, 0.40 ± 0.07, and 0.19 ± 0.06, respectively. High heritability estimates were observed for CEMA, IMF, P8FAT, and CWT of 0.52 ± 0.09, 0.61 ± 0.09, 0.55 ± 0.09, and 0.66 ± 0.09, respectively. Strong positive genetic correlations were found for FI with 200dWT, 400dWT, and 600dWT of 0.68 ± 0.09, 0.42 ± 0.11, and 0.61 ± 0.07, respectively. Weak genetic correlations were observed between RFI and growth traits. For carcass traits, genetic correlations between RFI and CEMA, IMF, CRIB, P8FAT, CWT were -0.19 ± 0.14, 0.31 ± 0.14, 0.18 ± 0.16, 0.24 ± 0.13, and 0.40 ± 0.12, respectively. There was a tendency for low to moderate unfavorable genetic associations between feed efficiency traits, evaluated as RFI and RG, with growth and carcass traits. This implies that selection for RFI would have slight negative impacts on growth and reduce carcass quality. To avoid this, it would be necessary to build selection indices to select feed efficient animals without compromising growth and meat quality.

The influence of maternal energy status during mid-gestation on growth, cattle performance, and the immune response in the resultant beef progeny

The objective of this experiment was to determine the effects of cow energy status during mid-gestation on progeny growth performance and health. To alter maternal energy status, cows (n = 151) were either fed to achieve or maintain BCS 5.0 to 5.5 (positive energy status) or fed at 80% of the energy requirements for BW maintenance (negative energy status) over the ensuing 91-d period of mid-gestation. Cows were managed as a common group beginning with the third trimester of gestation through subsequent weaning. Weaned calves (n = 71 steers and 61 heifers) were allotted to pens according to cow energy status during gestation and sex and stratified by BW to allow for live cattle performance evaluation. A subsample (n = 30) of calves was subjected to an ovalbumin challenge 19 d after entering the feedlot to compare antibody titer response. Mid-gestation dam energy status did not affect (P > 0.05) birth weight, weaning weight, or adjusted 205-d weaning weight of progeny. No differences (P > 0.05) were observed between treatments during the feeding period on ADG, DMI, and G:F. Ovalbumin results showed no interactions (P > 0.05) between treatments, days, or sexes, as well as no sex main effects. However, progeny of negative energy status cows had lower (P < 0.05) antibody titers in response to the ovalbumin challenge during the receiving period. These results suggest that differences in cow energy status applied during mid-gestation in this experiment will not affect BW or growth performance differences throughout the postnatal period in beef cattle progeny but may have an effect on the adaptive immune response during their receiving period in calves.

Assessment of progesterone profiles and postpartum onset of luteal activity in spring calving Hereford beef suckler cattle

BackgroundReproduction is the single greatest factor limiting beef cattle production. Previous research on beef suckler luteal activity has largely focused on the mechanisms, and duration, of postpartum anoestrus. However, the temporal pattern of luteal activity after resumption of post-partum ovarian activity, and the impact of pattern type on days open (DO) in purebred beef suckler cows, are unknown.MethodsProgesterone concentration was measured in milk samples taken thrice weekly from 120 lactations, in 87 animals, on 3 farms, over two years. Onset of luteal activity (OLA) was defined as the first day milk progesterone concentration exceeded 3 ng/ml for two successive measurements, or exceeded 5 ng/ml once. It was defined as delayed if it occurred more than 61 days postpartum. A short initial luteal phase consisted of progesterone concentrations which exceeded 3 ng/ml for fewer than 4 sequential measurements. Temporal progesterone patterns were classified as: 1) Normal cyclicity; 2) Cessation of luteal activity; 3) Prolonged luteal activity; 4) Erratic phase: failure to conform to 1, 2 or 3. Data concerning parity, previous calving interval, breeding values, calf birth and 200-d weight were obtained from the Norwegian Beef Cattle Recording System database.ResultsThe mean (SD) OLA was 41 d (20). Parity and calf birth weight were inversely correlated with OLA. Delayed OLA occurred in 14.4% of lactations. A short first luteal phase occurred in 61.5% of lactations, but this was unrelated to irregular luteal phase occurrence, pregnancy or DO. Irregular luteal phases occurred in 22% of lactations. The irregularities were: prolonged luteal phase (11%); cessation of luteal activity (5%); erratic luteal activity (6%). Early OLA was associated with prolonged luteal phases. DO was positively correlated with irregular luteal phases and negatively correlated with calf 200-d weight.ConclusionsThis study demonstrates that irregular luteal phases negatively affect reproductive performance in purebred beef suckler cattle. A moderate incidence of irregular luteal phases was seen in the study population. Whilst a positive relationship was seen between OLA and DO, unfavourable associations between early OLA and incidence of irregular luteal phases should be considered when developing breeding programmes.

Growth performances of F1 angus plus calves grazing on pasture in Hawaii’s tropical climate

Angus Plus cattle offer advantages for heat tolerance and forage utilization by introduction of Brangus and Brahman to Angus. To evaluate its adaptability in Hawaii Islands, we reported the growth performances of 213 F1 Angus Plus calve grazing on pasture. Least-square means of pre-weaning ADG ranged from 1,087 to 1,167 g in bull calves and from 1,030 to 1,048 g in heifer calves. The 205 d-adjusted weaning weight were 226 to 285 kg in bulls and 214 to 252 kg in heifers. The birth weight and hip height at birth were significantly correlated with weaning weight, 205 d-adjusted weaning weight, hip height at weaning and pre-weaning ADG (P < 0.01). Sire group significantly influenced pre-weaning growth performances through interaction with sex of calf. Bull calves from sire group of high growth were 1.0-3.8 kg heavier in birth weight than the bull calves from other sires (P < 0.001). Sire group x sex interaction was significant (P < 0.05) for calf birth weight, 205-d adjusted weaning weight and pre-weaning ADG. Sire group also played a significant role in hip height at birth (P < 0.05). Selections of the sires preferable for growth significantly improved calf pre-weaning growth performances.

Inheritance of pulmonary arterial pressure in Angus cattle and its correlation with growth1

Pulmonary arterial pressure (PAP) is an indicator of resistance to blood flow through the lungs and when measured at high altitude is a reliable predictor of susceptibility of an animal to brisket disease, a noninfectious cardiac pulmonary condition. (Co)-variance components for PAP, birth weight, and adjusted 205-d weaning weight were estimated from 2,305 spring-born, registered Angus cattle from a Colorado ranch at an elevation of 1,981 m. A single measure of PAP was collected after weaning on animals born from 1984 to 2003. The same licensed veterinarian measured every animal. Multitrait animal models with and without PAP maternal effects were fitted for a pedigree including 132 sires and 793 dams. The interaction of year x sex was a significant fixed effect (P <0.05) for PAP, but age of dam was not. Age at PAP testing was a significant (P <0.1) linear covariate for PAP, and scores increased 0.012 +/- 0.007 mmHg X d(-1) of age. Heritability of PAP direct was 0.34 +/- 0.05. Maternal heritability converged to a boundary at 0.0, and the model with maternal genetic effects for PAP was not significantly better than a model with only direct effects. Phenotypically, PAP was uncorrelated with birth or weaning weights. Genetically, PAP appeared to have positive, unfavorable relationships with direct effects for birth (0.49 +/- 0.12) and weaning weight (0.50 +/- 0.18). Positive correlations imply sires whose offspring exhibited resistance to brisket disease had lower weights and gains. A model that evaluated PAP in females and males as different traits had heritability estimates for each sex of 0.38 +/- 0.07 and 0.46 +/- 0.09, respectively, with a genetic correlation of 0.64 +/- 0.12 between the sexes and was not significantly better than the model assuming homogeneity by sex and a unit genetic correlation between sexes. The results suggest that PAP is moderately heritable in spring-born Angus cattle acclimatized and tested at high altitude, and selection for low PAP scores would be effective. Selection for growth at low altitude will produce cattle less suited to high altitude.

Effects of dry cow treatment of beef cows on pathogenic organisms, milk somatic cell counts, and calf growth during the subsequent lactation1

Spring calving Angus and Angus x Hereford multiparous cows were utilized to determine the effects of intramammary treatment with penicillin G procaine (200,000 IU) and novobiocin (400 mg) at the time of weaning on udder health and calf growth after the subsequent calving. Cows were stratified by age and breed and assigned randomly to receive intramammary treatment (n = 99) at weaning or as untreated controls (n = 97). Quarter milk samples were collected at weaning and at 8 to 14 d after calving. Milk samples were analyzed for somatic cell counts (SCC) and mastitis-causing bacteria. Dry cow treatment decreased (P = 0.005) the number of cows infected after calving. Treatment decreased (P = 0.04) the number of cows that developed new infections and reduced (P = 0.03) the number of quarters with mastitis-causing bacteria after calving that were infected at weaning. Somatic cell counts after calving were greatest (P = 0.008) for cows infected with Staphylococcus aureus. Treatment did not alter (P = 0.19) SCC of quarters after calving that were infected with S. aureus at weaning but reduced (P = 0.002) SCC after calving of quarters that were infected with coagulase-negative staphylococci at weaning. Body weight of calves during early lactation was increased (P = 0.006) if cows with intramammary infection were treated at weaning. Treatment of noninfected cows at weaning increased (P = 0.008) adjusted 205-d weaning weights of calves after the subsequent lactation when compared with untreated noninfected cows. We conclude that treatment of beef cows at weaning with intramammary antibiotics decreased intramammary infections after calving, improved udder health during the subsequent lactation, and increased BW gain of the calves.

Relationships between progeny residual feed intake and dam productivity traits

Two hundred and twenty-two yearling calves and their dams were used to examine the phenotypic (rp) relationships between progeny residual feed intake (RFI) and maternal productivity across 10 production cycles. Progeny RFI ranged from -3.95 to +2.72 kg as fed d-1 (SD = 0.94), while RFI adjusted for off-test backfat thickness (RFIadj), ranged from -2.48 to +1.53 kg as fed d-1 (SD = 0.88). Progeny RFI and RFIadj were unrelated to on-test age, body weight, growth rate, and ultrasound longissimus thoracis area and positively related to feed intake (rp = 0.51 to 0.53; P &lt; 0.001), feed to gain ratio (rp = 0.44 to 0.46; P &lt; 0.001), feeding behaviour traits (rp = 0.29 to 0.36; P &lt; 0.001) and cow RFI (rp = 0.30, P &lt; 0.05). Progeny RFI was positively related to measures of body fat (rp = 0.21 to 0.27; P &lt; 0.05), but these relationships disappeared when RFI was adjusted for off-test backfat thickness. Cows that had produced LOW (≤ 0.5 SD), MEDIUM (± 0.5 SD) or HIGH (≥ 0.5 SD) RFIadj progeny were similar in pregnancy (95.6 vs. 95.3 vs. 96.0%, P = 0.90), calving (84.9 vs. 83.4 vs. 86.3%, P = 0.62) and weaning (81.5 vs. 80.2 vs. 82.3%, P = 0.79) rates. However, cows that produced HIGH RFIadj progeny had a higher twinning rate (3.77 vs. 0.35 vs. 0.00%, P &lt; 0.001) and an increased calf death loss (8.06 vs. 4.24 vs. 4.02%, P = 0.10) compared with cows that produced MEDIUM or LOW RFIadj progeny. Cow body weight over 10 production cycles was similar at weaning, pre-calving and pre-breeding for dams that had produced LOW, MEDIUM and HIGH RFIadj progeny, and dams that produced LOW RFIadj progeny consistently averaged 2–3 mm more back fat thickness than dams that produced HIGH RFIadj progeny. Calf birth weight, pre-weaning ADG and 200-d weight, and cow production efficiency and calving interval were similar among dams that produced LOW, MEDIUM and HIGH RFIadj progeny. In addition, dams that produced LOW RFIadj progeny consumed less feed during their second trimester of pregnancy (10.9 vs. 11.6 vs. 12.2 kg DM d-1, P &lt; 0.05), had lower RFI values (-0.05 vs. 0.44 vs. 1.88 kg as fed d-1, P = 0.018) and calved later in the year (96 vs. 90 vs. 91 d Julian, P &lt; 0.001) than dams that produced MEDIUM and HIGH RFIadj progeny. These results showed that efficient RFI progeny and dams consumed less feed, had improved feed to gain ratio and spent less time in feed activity than inefficient cows and calves. In addition, cows that produced efficient calves were fatter, had fewer twins, less calf death loss and produced the same weight of calf weaned per cow exposed to breeding compared with cows that produced inefficient progeny. However, cows that produced efficient or low RFI progeny calved 5–6 d later in the year than cows that produced inefficient or high RFI progeny, indicating a need to monitor reproductive fitness in low RFI replacement heifers and breeding bulls. Key words: Residual feed intake, cow reproduction, lifetime production efficiency

Taxa de prenhez de vacas Nelore x Hereford em ambiente subtropical sob restrição alimentar

Foi desenvolvido um experimento para identificar os efeitos que influenciam a taxa de prenhez de 117 vacas de corte Nelore x Hereford aos 2 e 20 anos de idade e com diferentes frações gênicas de Nelore (25,0; 37,5; 50,0 e 100,0%), paridas no período de 11/08/03 a 23/12/03 e acasaladas, por monta natural, entre 10/12/03 e 12/03/04. Foram avaliados os efeitos dos fatores data juliana de parto (DJ), peso ao nascer (PN), sexo do bezerro (S) do parto anterior, ordem de parto (OP), altura de garupa (H), peso ao início do acasalamento (PI), escore de condição corporal ao início do acasalamento (ECCI), ganho diário médio de peso durante o acasalamento (GDA), fração gênica de Nelore (FGN) e peso ao desmame ajustado (PAJ205) do parto anterior sobre a probabilidade de prenhez e de concepção. Os dados foram submetidos à análise de regressão logística, por meio do procedimento LOGISTIC do pacote computacional SAS, para identificar os efeitos de cada variável. A média da taxa de prenhez foi de 43,2%. A probabilidade de prenhez e as chances de concepção foram explicadas pelas variações de DJ, PI, ECCI e GDA. A mudança na chance de prenhez para cada acréscimo na variável regressora foi estimada com base na estatística da razão entre chances (odds ratio), determinada por OR = exp(b k), considerando que chance é a razão entre a probabilidade de o evento ocorrer e a de não ocorrer. Não foram observados efeitos significativos de PN, S, OP, H, FGN e PAJ205. Portanto, para aumentar as taxas de prenhez de vacas de corte, são necessárias melhorias no escore de condição corporal (ECC) no início do acasalamento e no ganho de peso (GP) durante a estação de monta, ambos decorrentes de adequada nutrição pré e pós-parto.

Age of dam and sex of calf adjustments and genetic parameters for gestation length in Charolais cattle1

To estimate adjustment factors and genetic parameters for gestation length (GES), AI and calving date records (n = 40,356) were extracted from the Canadian Charolais Association field database. The average time from AI to calving date was 285.2 d (SD = 4.49 d) and ranged from 274 to 296 d. Fixed effects were sex of calf, age of dam (2, 3, 4, 5 to 10, > or = 11 yr), and gestation contemporary group (year of birth x herd of origin). Variance components were estimated using REML and 4 animal models (n = 84,332) containing from 0 to 3 random maternal effects. Model 1 (M1) contained only direct genetic effects. Model 2 (M2) was G1 plus maternal genetic effects with the direct x maternal genetic covariance constrained to zero, and model 3 (M3) was G2 without the covariance constraint. Model 4 (M4) extended G3 to include a random maternal permanent environmental effect. Direct heritability estimates were high and similar among all models (0.61 to 0.64), and maternal heritability estimates were low, ranging from 0.01 (M2) to 0.09 (M3). Likelihood ratio tests and parameter estimates suggested that M4 was the most appropriate (P < 0.05) model. With M4, phenotypic variance (18.35 d2) was partitioned into direct and maternal genetic, and maternal permanent environmental components (hd2 = 0.64 +/- 0.04, hm2 = 0.07 +/- 0.01, r(d,m) = -0.37 +/- 0.06, and c2 = 0.03 +/- 0.01, respectively). Linear contrasts were used to estimate that bull calves gestated 1.26 d longer (P < 0.02) than heifers, and adjustments to a mature equivalent (5 to 10 yr old) age of dam were 1.49 (P < 0.01), 0.56 (P < 0.01), 0.33 (P < 0.01), and -0.24 (P < 0.14) d for GES records of calves born to 2-, 3-, 4-, and > or = 11-yr-old cows, respectively. Bivariate animal models were used to estimate genetic parameters for GES with birth and adjusted 205-d weaning weights, and postweaning gain. Direct GES was positively correlated with direct birth weight (BWT; 0.34 +/- 0.04) but negatively correlated with maternal BWT (-0.20 +/- 0.07). Maternal GES had a low, negative genetic correlation with direct BWT (-0.15 +/- 0.05) but a high and positive genetic correlation with maternal BWT (0.62 +/- 0.07). Generally, GES had near-zero genetic correlations with direct and maternal weaning weights. Results suggest that important genetic associations exist for GES with BWT, but genetic correlations with weaning weight and postweaning gain were less important.

Genetic parameters for a maternal breeding goal in beef production1

New maternal breeding values have been developed for use in UK beef evaluations. To undertake multitrait BLUP evaluations, it is necessary to have a full covariance matrix. This study outlines the approach taken to construct the full covariance matrices for the four beef breeds that most widely contribute to suckler beef cows in the United Kingdom. The maternal traits investigated were age at first calving, calving interval, lifespan, mature cow weight, 200-d weight, and calving difficulty. Three terminal sire traits (weight at 400 d, ultrasonic fat depth, and muscle score) were included to estimate covariances between the new and existing traits. A sire-maternal-grandsire model was used for the estimation procedure in a series of bivariate and multivariate models. A weighted bending procedure was employed to construct positive definite covariance matrices. Parameter estimates broadly agreed with literature values, although for some traits, literature information was very scarce. Some differences between parameters for different breeds were evident.

Relationship of sire expected progeny differences to milk yield in Brangus cows1,2

Milk yield from 160 Brangus cows sired by 65 Brangus bulls was measured over a 3-yr period with a single-cow milking machine to estimate the relationship of actual milk yield of daughters and their calves' BW with cow sire EPD for milk during the preweaning period. Milk yield was measured six times per year at an average 49, 78, 109, 138, 168, and 198 d postpartum. The regression of daughters' milk yield on sire milk EPD was quadratic (P < 0.01), and the initial linear portion of the curve differed among months (P < 0.05) at an average cow BW. Similarly, the regression of 6-mo average 24-h milk yield on sire milk EPD was curvilinear (P < 0.05). When cow BW was fitted as a covariate in the regression of 6-mo average 24-h milk yield on sire milk EPD, there was an interaction of cow BW with linear sire milk EPD and quadratic sire milk EPD (P < 0.10). The associated response surface suggested that the regression was primarily linear in cows weighing < or = 520 kg and curvilinear in cows weighing >520 kg. A trend existed for the regression of calf 205-d weight on grandsire milk EPD to be curvilinear (P < 0.21); however, the regression of calf 205-d weight on milk yield of their dam was linear (P < 0.01). Results from these data suggest that genetic potential for milk yield, and possibly the associated effects on calf BW transmitted through the grandsire, may have a practical maximum because of nutritional limitations that prevent the expression of genetic potential beyond that level, particularly in heavier cows, which suggests the need to match sire milk EPD and cow BW with production environment.

Genetic evaluation of the ratio of calf weaning weight to cow weight1,2,3

The phenotypic ratio of a calf's weaning weight to its dam's weight is thought to be an indicator of efficiency of the cow. Thus, the objectives of this research were to 1) estimate genetic parameters for the ratio of 200-d calf weight to mature-equivalent cow weight at weaning, its components, and other growth traits; and 2) evaluate responses to selection based on the ratio. Phenotypes evaluated were the ratio (100 kg/ kg; n = 4,184), birth weight (kg; n = 5,083), 200-d weight (kg; n = 4,902), 365-d weight (kg; n = 4,626), and mature-equivalent cow weight at weaning (kg; n = 4,375). In 1989, a randomly selected and mated control line and a line selected for greater values of the ratio were established. Average generation intervals were 3.39 +/- 0.05 and 3.90 +/- 0.08 yr in the ratio selected line and control line, respectively. The ratio selection line (n = 895) accumulated approximately 4.7 SD more selection differential than the control line (n = 912) over 2.5 generations. Data were analyzed with a multiple-trait Gibbs sampler for animal models to make Bayesian inferences. Heritability estimates (posterior mean +/- SD) for direct effects were 0.20 +/- 0.03, 0.46 +/- 0.04, 0.48 +/- 0.03, 0.58 +/- 0.04, and 0.76 +/- 0.02 for ratio, birth weight, 200-d weight, 365-d weight, and cow weight, respectively. Estimates for heritability of maternal effects were 0.58 +/- 0.05, 0.10 +/- 0.02, 0.13 +/- 0.02, and 0.10 +/- 0.02 for ratio, birth weight, 200-d weight, 365-d weight, respectively. Significant response to selection was limited to maternal effects: 1.32 +/- 0.38 ratio units per generation. As the ratio was a trait of the calf, estimated maternal genetic effects on the ratio contained both genetic effects due to dams that environmentally affected progeny performance and direct effects on the reciprocal of cow weight. In the control line, genetic trends in direct and maternal 200-d weight were -1.28 +/- 0.91 and 0.62 +/- 0.92 kg/generation, respectively, and the genetic trend in direct effects on cow weight was -5.72 +/- 2.80 kg/ generation. In the selection line, genetic trends in direct and maternal 200-d weight were 1.43 +/- 0.79 and 2.90 +/- 0.80 kg/generation and the genetic trend in cow weight was -2.79 +/- 2.43 kg/generation. Significant correlated responses were observed in direct effects on birth weight and maternal effects on 365-d weight. Results contraindicate use of the ratio of calf weaning weight to cow weight as a selection criterion.

Genetic parameters among growth and carcass traits of Canadian Charolais cattle

Genetic parameters for three growth and five carcass traits were estimated for Charolais using a combination of carcass progeny test, purebred field performance and pedigree data. Heritabilities and genetic and residual correlations were derived from variance components for birth weight (BWT, n = 54 221), 205-d weaning weight (WT205, n = 31 384), postweaning gain (PWG, n = 19 403), hot carcass weight (HCW, n = 6958), average subcutaneous fat thickness (FAT, n = 6866), longissimus muscle area (REA, n = 6863), marbling score (MAR, n = 6903) and estimated carcass lean yield percentage (PLY, n = 6852) with an animal model (n = 78 728) and restricted maximum likelihood. Breed of dam and contemporary group appropriate to each trait were included as fixed effects in the model, whereas random effects included direct genetic for all traits, maternal genetic for BWT and WT205, and maternal permanent environmental for WT205. Carcass traits were adjusted to a constant harvest age of 425 d. Heritability estimates of 0.53, 0.22, and 0.21 were obtained for direct components of BWT, WT205, and PWG, respectively, and maternal heritabilities were 0.16 and 0.10 for BWT and WT205, respectively. Direct × maternal genetic correlations for BWT (-0.49) and WT205 (-0.35) were negative. Heritabilities for HCW, FAT, REA, MAR, and PLY were 0.33, 0.39, 0.43, 0.34, and 0.46, respectively. Genetic correlations among direct effects for growth traits were moderately positive and generally uncorrelated with maternal effects across traits. Lean and fat deposition in the carcass generally had negative, unfavorable genetic correlations, although improvement in lean yield and marbling score may not be strongly antagonistic. Genetic correlations of direct and maternal components of growth traits with carcass traits suggested that selection for increased growth rate would not be antagonistic to improvement in carcass yield or meat quality. Key words: Carcass, Charolais, correlation, genetic parameters, growth

Using Adjusted 205-d Weight Ratios to Predict Beef Cow-Calf Performance12

Eighteen cow-calf herds were used to determine beef cow performance predictability over time to evaluate the effectiveness of Cooperative Extension recommendations on increasing calf preweaning growth performance, and to assess cooperators’ implementation of these recommendations. The data set included 8928 cow records, of which 4379 and 1958 cows had performance records for 2 and 3 consecutiveyr, respectively. For each cow herd, adjusted 205-d BW and ratios were calculated within calf gender. Cows within herds were ranked in descending order based on calf-adjusted 205-d weight ratios and then divided into three groups (top, middle, and bottom thirds). When comparing the cows’ consecutive years’ rankings, year and cow age were not significant (P> 0.10). Of the cows that ranked in the top one-third inyr 1, 33% ranked in the top one-third for the next 2 consecutiveyr, and 71% ranked in the top one-third at least 1yr of the next 2yr. Among the cows ranking in the bottom one-third inyr 1, 27% ranked in the bottom one-third for the next 2 consecutiveyr, and 63% ranked in the bottom one-third at least once in the next 2 consecutiveyr. The correlations between dam’s BW and weaning BW efficiency and metabolic efficiency across herds were all negative and ranged from -0.70 to -0.45 and -0.61 to -0.21, respectively. These results support the practice of culling cows, even first-calf heifers that rank in the bottom one-third of the herd, based on calf preweaning growth performance after 1yr.

Maternal and reproductive performance of Brahman x Angus, Senepol x Angus, and Tuli x Angus cows in the subtropics.

To determine the maternal and reproductive performance of F1 cows in the subtropics, 42 Brahman x Angus, 34 Senepol x Angus, and 50 Tuli x Angus cows were bred to Angus bulls to calve first and subsequently bred to Charolais bulls to calve as 3- to 8-yr-olds. Age at first calving did not differ among crossbred cows. Angus-sired calf birth weights were heavier (P < 0.01) from Senepol x Angus than either Brahman x Angus or Tuli x Angus cows. Weaning weights of Angus-sired calves were heavier (P < 0.01) from Brahman x Angus (213.5 kg) than either Senepol x Angus (194.9 kg) or Tuli x Angus (191.5 kg) cows. As 3- to 8-yr-old cows, calf birth weights were heavier (P < 0.05) from Senepol x Angus compared with Brahman x Angus but not Tuli x Angus cows. Weaning weights of Charolais-sired calves were heaviest (P < 0.05) from Brahman x Angus cows (268.9 kg), lightest from Tuli x Angus cows (233.4 kg), and intermediate from Senepol x Angus cows (245.0 kg). Calf crop born and calf crop weaned were lowest (P < 0.05) for Senepol x Angus cows (76.9 and 70.2%) and did not differ between Brahman x Angus (89.0 and 86.1%) and Tuli x Angus (94.7 and 86.5%) cows. Tuli x Angus cows tended (P < 0.10) to have a lower percentage of unassisted births and lower (P < 0.10) calf survival to weaning than Brahman x Angus cows but not Senepol x Angus cows. As 3- to 8-yr-olds, weaning weight per cow exposed was greatest (P < 0.05) for Brahman x Angus (234.2 kg), least (P < 0.05) for Senepol x Angus (173.0 kg), and intermediate (P < 0.05) for Tuli x Angus (209.1 kg) cows. Also as 3- to 8-yr-olds, efficiency (205-d calf weight per 100 kg of cow exposed) was similar for Brahman x Angus (42.2) and Tuli x Angus cows (40.7), and both were greater (P < 0.01) than for Senepol x Angus cows (33.8). These data indicate that, in the subtropics, maternal and reproductive performance of Tuli x Angus cows, but not Senepol x Angus cows, was comparable to Brahman x Angus cows, except for lower calf survivability and weaning weight.