Kilograms Of Calf Research Articles

182 Converting spring-born heifers into a summer-calving herd increases subsequent cow longevity and productivity

Abstract Developing replacement heifers is one of the most expensive and complex management decisions for a cow-calf producer, which also has long-term implications for profitability. The objective of this study was to determine the impact of converting spring-born heifers into a summer-calving herd on growth, reproductive performance, longevity, and productivity compared with early or late-born May heifers. Over a 3 yr period, Red Angus/Simmental crossbred heifers (n = 273) were utilized to determine the impact of converting March-born heifers (Convert; n = 90) to a May-calving herd compared with May-born heifers on reproductive performance, body weight (BW), and calf performance from a yearling to 5 yr of age. May-born heifers were retrospectively grouped into 2 different groups: heifers born in the first 21 d of calving as a heifer calf (Early; n = 123) or heifers born after the 21 d of calving as a heifer calf (Late; n = 60). Heifers were exposed to bulls for a 45-d breeding season with a bull-to-heifer ratio of 1:20. Heifers were synchronized with a single injection of prostaglandin F2α (5-mL i.m.; Lutalyse, Zoetis, Parsippany, NJ) 5 d after bulls were introduced in the pasture for breeding. Data were analyzed as a randomized design using the MIXED procedure (SAS Inst. Inc., Cary, NC, USA). All binomial data were analyzed using PROC GLIMMIX. Heifer served as the experimental unit with treatment and year developed set as fixed effects. Heifer BW at December, May, July, and pregnancy check (Oct) were greater (P < 0.01) for Convert heifers with no difference between Early and Late born heifers. Heifer BCS at pregnancy check was not different (P = 0.13) among heifer treatment groups. However, pregnancy rate tended (P = 0.08) to increase for Convert heifers with no difference between Early and Late born May heifers. After 5 yr of age, retention rate was increased (P = 0.04) in Convert cows compared with Early and Late May-born cows with no difference (P = 0.84) between the two May-born heifer groups. Total kilograms of calf weaned was greater (P = 0.04) in Convert cows than their counterparts with no differences (P = 0.94) between Early and Late May-born cows. This study implies that selecting replacement heifers from an earlier calving season for replacements in a later calving season increases the longevity and long-term productivity of the cowherd than selecting heifers within the same calving season. This may be even more important in resource-poor breeding environments that create reproductive challenges for heifers and rebreeding young cows.

Body mass index at calving on performance and efficiency of Charolais cow herds.

This study evaluated the productive and reproductive performance of Charolais cows with different body mass index (BMI) at calving and the development of their calves. Seventy-two Charolais cows and their calves were grouped into BMI classes at calving, namely, low, moderate, and high. Body mass index was determined by dividing the cows' body weight by their body length and hip height and finally dividing the result by 10. Cows and their calves were weighed immediately after calving, at early weaning (63-day postpartum), and at pregnancy diagnosis (210-day postpartum). To evaluate milk production and quality, collections were performed at 21, 42, and 63days after calving. Cows with high and moderate BMI were heavier (P < 0.05) than low-BMI cows from calving to the date of pregnancy diagnosis. Calves from low-BMI cows were heavier (P < 0.05) at 210-day postpartum than those born to cows with moderate and high BMI. The low- and moderate-BMI cows had higher pregnancy rates than those with a high BMI and were more efficient (P < 0.05) at calving and at weaning in kilograms of calf produced per kilogram of cow kept in the herd. High- and moderate-BMI cows had the highest milk production, whereas low-BMI cows produced milk with the highest concentrations of lactose and solids-not-fat (P < 0.05). Charolais cows with low and moderate BMI at calving are more efficient in production systems. The BMI may be considered a selection variable to improve the productive results of breeding herds.

Body mass index at calving on performance and efficiency of Zebu cow herds

This study examines the impact of the body mass index (BMI) at calving on the development and postpartum efficiency of cows of Zebu origin. The study involved 87 cows and their calves [pure Nellore (N) or predominant Nellore composition in a cross with Charolais (C) (3/4N1/4C and 5/8N3/8C)]. The mothers were grouped into classes according to their BMI at calving, namely, ‘small’, ‘moderate’ and ‘large’. Body mass index was determined by dividing the body weight of the cows by their length and by hip height and then dividing the result by 10. Cows were weighed at calving, at weaning, at the end of the breeding period and at the diagnosis of pregnancy. Calves were weighed at birth, at early weaning (63 days) and at 210 of age. To evaluate milk yield and quality, milk was collected at 21, 42 and 63 days after calving. Milk yield was measured by the direct method, with manual milking, followed by analysis of the lactose, fat, total solids and crude protein contents. Pregnancy rate was similar between the three BMI groups; however, cows with a lower BMI were more efficient at calving in producing kilograms of calf per kilogram of cow kept. Higher BMI provide higher milk yields, without affecting its quality, as well as heavier calves at early weaning and at 210 days of age.

Effects of body condition score at initiation of the breeding season on reproductive performance and overall productivity of Bos taurus and B. indicus beef cows

This experiment was conducted to evaluate reproductive and productive responses of Bos indicus and B. taurus beef cows according to body condition score (BCS) at initiation of the annual breeding season. Non-pregnant, suckling multiparous cows were assigned to a fixed-time artificial insemination treatment regimen followed by natural service. Cows were classified as having a BCS < 5.0 (B. taurus, n = 158; B. indicus, n = 248) or BCS ≥ 5.0 (B. taurus, n = 173; B. indicus, n = 122). Calving rate was greater (P < 0.03) in cows with a BCS ≥ 5.0 (93.7 % and 85.1 % in B. taurus, 83.6 % and 73.3 % in B. indicus), which also calved earlier (P < 0.01) compared with cows with a BCS < 5.0. Cows with a BCS ≥ 5.0 weaned more (P ≤ 0.05) calves compared with those with a BCS < 5.0, which were older (P ≤ 0.04) and weighed more (P ≤ 0.09) at weaning (258 and 252 kg in B. taurus, 213 and 203 kg in B. indicus). Kilograms of calf weaned/cow in the breeding herd were greater (P ≤ 0.03) in cows with a BCS ≥ 5.0 compared with those with a BCS < 5.0 (221 and 200 kg in B. taurus, 159 and 129 d in B. indicus). Collectively, cows with a BCS ≥ 5.0 at initiation of the breeding season had greater reproductive and overall productivity during a cow-calf cycle, and these outcomes were observed in B. taurus and B. indicus cowherds.

Body size in beef cows and its influence on calf production

Cattle farming becomes more intensive when the productive efficiency of the cows is increased, and nutrition is adjusted to the animal biotype. Eighty purebred Charolais and Nellore cows and their crosses between 3 and 7 years of age, were grouped for body weight at calving into Light (332.6 kg), Moderate (385.3 kg) and Heavy (444.6 kg). Cows and their calves were weighed at calving, at 63 days (early weaning) and at 210 days. The estimated milk production of the cows was evaluated by manual milking at 21, 42 and 63 days postpartum. The difference in the weight of the cows at calving was maintained during lactation and at 210 days postpartum. The body size of the cow did not influence milk production. Heavier cows produce heavier calves up to 365 days of age compared to lighter cows. The reproductive performance of the cows is not affected by their weight. The production of kilograms of calf for every 100 kilograms of cow at calving and weaning is higher in Light cows. The production of kilograms of calf adjusted for the pregnancy rate of the cows is higher in Heavy cows. Production efficiency in kilograms of calf per area is lower in Heavy cows.

Effect of live weight of beef cows on calf production efficiency

The objective was to evaluate the development and reproductive performance of beef cows of different body weights at calving were evaluated. Milk yield and calf production efficiency were assessed in secundiparous Braford cows classified at calving according to weight as Light (325.2±3.7 kg), Moderate (347.7±4.0 kg), and Heavy (384.2±4.1 kg). Heavy cows had higher total milk yield than Light cows, but did not differ from Moderate, reflecting in calves weighing at weaning 82.1, 76.6, and 76.9 kg, respectively. Differences on pregnancy rates for Light (90.0%, 18 pregnant cows/2 of eligible cows), Moderate (70.2%, 12 pregnant cows/5 of eligible cows), and Heavy (62.5%, 10 pregnant cows/6 of eligible cows) were not detected. Light cows were more productive and efficient when production performance was adjusted for the pregnancy rates than Moderate and Heavy cows. Production of kilograms of calves adjusted for pregnancy was 20.5, 16.2±0.5, and 14.0±0.5 kg for the Light, Moderate, and Heavy cows, respectively. Heavy and Moderate cows were less efficient as compared with the Light ones for production of calves adjusted for their calving interval. Light cows produce more kilograms of calf/cow, requiring the same amount of milk to produce one kilogram of calf. Light cows also have higher efficiency converting milk into calf weight than Moderate and Heavy cows. The productivity and efficiency of breeding herds should be evaluated by the combination of pregnancy rate and kilograms of weaned calves per cow exposed to breeding.

&lt;b&gt;Body size and its effects on productive efficiency of cows with predominant Nellore genetic composition

This study was developed to evaluate productive efficiency during the lactation period of cows with predominant Nellore genetic composition based on their body size. Cows were divided into the following categories: light (≤ 316 kg), moderate (≥ 317 and ≤ 400 kg), or heavy (≥ 401 kg). Body weight change and total gain from birth to 210 days of age of calves born from heavy cows (0.155±0.03 and 111.6±5.1 kg) were higher than those of calves born from light (0.064±0.03 and 91.0±4.3 kg) and moderate (0.144±0.03 and 97.7±4.0 kg) cows. Calf production index differed (p &lt; 0.05) with the herd of heavy cows (93.5±3.2 kg), producing 57.4 and 19.7% more kilograms of calf than light (59.4±2.7 kg) and moderate (78.1±2.4 kg) cows, respectively. Heavy Nellore cows produce heavier calves and have a better reproductive performance, which lead to a better calf production index. However, they require a larger area for the same herbage allowance. Calves born from heavier Nellore cows gain more weight from birth to 210 days of age and are heavier from 210 to 270 days of age.

Performance Efficiency of Pasture-raised Primiparous Beef Cows of Three Different Biotypes and Two Milk Production Levels

Background: Productivity and efficiency of beef production systems should be estimated based on cow size, calf growth rate and cow reproduction rate, which are critical factors for the evaluation of production characteristics of beef cattle of different biological types. One of the ways to measure beef cow productivity is based on the ratio of calf weaning weight to cow weight. The purpose of this study was to evaluate the performance and reproductive efficiency of primiparous beef cows of three different biotypes and two milk production levels, from calving to weaning, in pasture-raised beef systems. Materials, Methods &amp; Results: Forty-two primiparous Angus cows were classified according to body weight at calving, as follows: Heavy (431 kg); Medium (388 kg); and Light (348 kg). Cow efficiency as a function of biotype was evaluated at two different moments: calving and weaning, based on the ratio of calf weight to cow weight*100 (in kilograms). Calf production efficiency was determined based on the ratio of calf weaning weight (CWW) to cow pregnancy rate (PR), resulting in the calf production index = kg of weaning calves per cow (CWW*PR/100). The experimental design was a completely randomized factorial 3 x 2 x 2 design (three biotypes x two calf sexes x two milk production levels). The results were subjected to ANOVA and F-test. The Light and Medium cow groups produced more (P &lt; 0.05) kilograms of calf per kilogram of cow (16.0 and 15.1 kg, respectively) than the Heavy group (14.0 kg). Light cows showed lower (P &lt; 0.05) milk production and, as a result, lighter (P &lt; 0.05) calves at weaning (151.9 ± 4.3 kg) than Medium and Heavy groups, 166.0 ± 3.7; 166.5 ± 4.0 kg, respectively. At beginning of the breeding season, cows of the Lower milk production group were on average 27.49 kg heavier than cows in the Higher milk production group. There was an interaction (P &lt; 0.05) between total milk production and calf sex on characteristics of performance in calves and performance efficiencies of the system. Light and Medium cows showed 51 and 25 kg total weight gain from calving to weaning, corresponding to 14.7 and 6.4% of body weight, respectively. The Heavy group, however, showed a 3 kg loss (0.5% of body weight) during the same period. Discussion: A higher growth rate was observed in the pre-weaning period of the calves of heavy cows; as a result, these calves were heavier at weaning. To achieve this result, heavier cows may compensate this higher nutritional requirement using body reserves. This biological adjustment may not be economically efficient, since the subsequent reproduction of these cows could be impaired by increases in milk production. Therefore, the target cow in a pasture-raised beef system is one whose low nutritional requirements enable her to produce milk, resulting in heavier calves, and whose physiological conditions enable her to conceive again during the breed season. Light cows can be considered an efficient group, since their pregnancy rate enabled them to create a positive difference for the group, notwithstanding their lower milk production and lighter calves (P &lt; 0.05) at weaning. This tendency is expected, since increased growth rates are associated with a decrease in puberty and early finishing age. It is essential to select animals according to their efficiency in order to reduce the cow’s requirements, since this favors the increased productivity of cows of lower maintenance cost in relation to their body weight, leading to higher biological and economic efficiency in the beef production system. In conclusion, because of their lower nutritional requirements, cows of small and moderate biotypes and lower total milk production are more efficient than cows of larger biotypes and higher milk production in pasture-raised beef systems.

A deterministic, dynamic systems model of cow-calf production: The effects of breeding replacement heifers before mature cows over a 10-year horizon.

Some cattle production experts believe that cow-calf producers should breed replacement heifers (nulliparous cows) before cows (primiparous and multiparous cows), sometimes referred to as providing a heifer lead time (tHL). Our objective was to model the effects different durations of tHL may have on measures of herd productivity, including the percent of the herd cycling before the end of the first 21 d of the breeding season (%C21), the percent of the herd pregnant at pregnancy diagnosis (%PPD), the distribution of pregnancy by 21-d breeding intervals, the kilograms of calf weaned per cow exposed (KPC), and the replacement percentage (%RH), using a deterministic, dynamic systems model of cow-calf production over a 10-yr horizon. We also wished to examine differences in the effect of tHL related to the primiparous duration of postpartum anestrus (dPPA). The study model examined 6 different dPPA for primiparous cows (60, 70, 80, 90, 100, or 110 d). The multiparous cow duration of postpartum anestrus was set to 60 d. The breeding season length for nulliparous cows was 63 d, as was the breeding season length for primiparous and multiparous cows. Nulliparous cows were modeled with a tHL of 0, 7, 14, 21, 28, 35, or 42 d. Results are reported for the final breeding season of the 10-yr horizon. Increasing tHL resulted in a greater %C21 for the herd and for primiparous cows. Length of tHL had minimal impact on the %PPD unless the dPPA was 80 d or greater. For a dPPA of 110 d, a 0 d tHL resulted in the herd having 88.1 %PPD. When tHL was 21 d, the %PPD increased to 93.0%. The KPC was 161.2 kg when the dPPA was 110 d and tHL was 0 d and improved to 183.2 kg when tHL was increased to 42 d. The %RH did not vary much unless the dPPA was 90 d or greater, but increasing tHL resulted in decreased %RH. Based on the model results, increasing tHL improves the production outcomes included in the analysis, but herds with dPPA of 90 d or greater had the greatest degree of improvement. For these herds, approximately two-thirds of the improvement in outcomes by increasing tHL from 0 d to 42 d was realized when tHL was 21 d. Costs are likely incurred when implementing tHL in a breeding management program, and an ideal tHL likely depends on the dPPA of the herd, the expected improvement in productivity, and the costs associated with increasing tHL. Determining the dPPA of a herd could help veterinarians and producers develop optimal herd management strategies.

A deterministic, dynamic systems model of cow-calf production: The effects of the duration of postpartum anestrus on production parameters over a 10-year horizon

The duration of postpartum anestrus (dPPA) is important to consider for reproductive performance and efficiency in cow-calf operations. We developed a deterministic, dynamic systems model of cow-calf production over a 10-yr horizon to model the effects that dPPA had on measures of herd productivity, including the percentage of cows cycling before the end of the first 21 d of the breeding season (%C21), the percentage of cows pregnant at pregnancy diagnosis (%PPD), the distribution of pregnancy by 21-d breeding intervals, the kilograms of calf weaned (KW), the kilograms of calf weaned per cow exposed (KPC), and the replacement percentage. A 1,000-animal herd was modeled, with the beginning and ending dates for a 63-d natural service breeding season being the same for eligible replacement heifers (nulliparous cows) and cows (primiparous and multiparous cows). Herds were simulated to have a multiparous cow dPPA of 50, 60, 70, or 80 d, with the dPPA for primiparous cows being set to 50, 60, 70, 80, 90, 100, or 110 d. Only combinations where the primiparous dPPA was greater than or equal to the multiparous dPPA were included, resulting in 22 model herds being simulated in the analysis. All other model parameters were held constant between simulations. In model season 10, the %C21 was 96.2% when the multiparous cow and primiparous cow dPPA was 50 d and was 48.3% when the multiparous cow and primiparous cow dPPA was 80 d. The %PPD in model season 10 for these same herds was 95.1% and 86.0%, respectively. The percentage of the herd becoming pregnant in the first 21 d of the breeding season also differed between these herds (61.8% and 31.3%, respectively). The 10-yr total KW was more than 275,000 kg greater for the herd with a 50-d multiparous cow and primiparous cow dPPA when compared with the herd with the 80-d multiparous and primiparous cow dPPA and had a model season 10 KPC of 180.8 kg compared with 151.4 kg for the longer dPPA. The model results show that both the multiparous cow and primiparous cow dPPA affect herd productivity outcomes and that a dPPA less than 60 d results in improved production outcomes relative to longer dPPA. Veterinarians and producers should consider determining the dPPA to aid in making management decisions to improve reproductive performance of cow-calf herds.

Productive efficiency of cows primiparous aberdeen angus of the body size and milk production levels

Assessment of the productive efficiency of 30 primiparous Aberdeen Angus cows of different body sizes, classified at calving as heavy (375±10.5 kg) or light (283±7.7 kg), and different total milk-yield levels, classified as high (868±24.5 kg) or low (547±18.3 kg). Heavy cows were superior in weight at calving and weaning, but there were no differences in milk yield and weight at birth and weaning of calves. Heavy cows were less efficient than light cows in the production of kilograms of calves per 100 kg of cows at calving and at weaning. High-producing cows were heavier at calving and had heavier calves at birth and weaning, but did not differ between the milk-yield levels for the variation in daily weight. The variation in daily weight of the calves was greater from high-producing cows. High-producing dairy beef cows were more efficient at weaning, and their calves required less milk to produce one kilogram of live weight.

Bill E. Kunkle Interdisciplinary Beef Symposium: Temperament and acclimation to human handling influence growth, health, and reproductive responses in Bos taurus and Bos indicus cattle.

Temperament in cattle is defined as the fear-related behavioral responses when exposed to human handling. Our group evaluates cattle temperament using 1) chute score on a 1 to 5 scale that increases according to excitable behavior during restraint in a squeeze chute, 2) exit velocity (speed of an animal exiting the squeeze chute), 3) exit score (dividing cattle according to exit velocity into quintiles using a 1 to 5 scale where 1=cattle in the slowest quintile and 5=cattle in the fastest quintile), and 4) temperament score (average of chute and exit scores). Subsequently, cattle are assigned a temperament type of adequate temperament (ADQ; temperament score≤3) or excitable temperament (EXC; temperament score>3). To assess the impacts of temperament on various beef production systems, our group associated these evaluation criteria with productive, reproductive, and health characteristics of Bos taurus and Bos indicus-influenced cattle. As expected, EXC cattle had greater plasma cortisol vs. ADQ cattle during handling, independent of breed type (B. indicus×B. taurus, P<0.01; B. taurus, P<0.01; B. indicus, P=0.04) or age (cows, P<0.01; heifers or steers, P<0.01). In regards to reproduction, EXC females had reduced annual pregnancy rates vs. ADQ cohorts across breed types (B. taurus, P=0.03; B. indicus, P=0.05). Moreover, B. taurus EXC cows also had decreased calving rate (P=0.04), weaning rate (P=0.09), and kilograms of calf weaned/cow exposed to breeding (P=0.08) vs. ADQ cohorts. In regards to feedlot cattle, B. indicus EXC steers had reduced ADG (P=0.02) and G:F (P=0.03) during a 109-d finishing period compared with ADQ cohorts. Bos taurus EXC cattle had reduced weaning BW (P=0.04), greater acute-phase protein response on feedlot entry (P≤0.05), impaired feedlot receiving ADG (P=0.05), and reduced carcass weight (P=0.07) vs. ADQ cohorts. Acclimating B. indicus×B. taurus or B. taurus heifers to human handling improved temperament (P≤0.02), reduced plasma cortisol (P<0.01), and hastened puberty attainment (P≤0.02). However, no benefits were observed when mature cows or feeder cattle were acclimated to human handling. In conclusion, temperament impacts productive, reproductive, and health characteristics of beef cattle independent of breed type. Hence, strategies to improve herd temperament are imperative for optimal production efficiency of beef operations based on B. taurus and B. indicus-influenced cattle.

Effects of temperament and acclimation to handling on reproductive performance of Bos taurus beef females1

Two experiments evaluated the effects of temperament and acclimation to handling on reproductive performance of Bos taurus beef females. In Exp. 1, 433 multiparous, lactating Angus × Hereford cows were sampled for blood and evaluated for temperament before the breeding season. Cow temperament was assessed by chute score and exit velocity. Chute score was assessed on a 5-point scale according to behavioral responses during chute restraining. Exit score was calculated by dividing exit velocity into quintiles and assigning cows with a score from 1 to 5 (1 = slowest, 5 = fastest cows). Temperament score was calculated by averaging chute and exit scores. Cows were classified for temperament type according to temperament score (≤ 3 = adequate, > 3 = aggressive). Plasma cortisol concentrations were greater (P < 0.01) in cows with aggressive vs. adequate temperament. Cows with aggressive temperament had reduced (P ≤ 0.05) pregnancy and calving rate and tended to have reduced (P = 0.09) weaning rate compared with cows with adequate temperament. Hence, kilogram of calf born per cow was reduced (P = 0.05) and kilogram of calf weaned per cow tended to be reduced (P = 0.08) in aggressive cows. In Exp. 2, 88 Angus × Hereford heifers (initial age = 206 ± 2 d) were weighed (d 0 and 10) and evaluated for temperament score (d 10). On d 11, heifers were ranked by these variables and assigned to receive or not (control) an acclimation treatment. Acclimated heifers were processed through a handling facility 3 times weekly for 4 wk (d 11 to 39; Mondays, Wednesdays, and Fridays), whereas control heifers remained undisturbed on pasture. Heifer puberty status, evaluated via plasma progesterone concentrations, was assessed on d 0 and 10, d 40 and 50, 70 and 80, 100 and 110, 130 and 140, 160 and 170, and 190 and 200. Blood samples collected on d 10 and 40 were also analyzed for plasma concentrations of cortisol and haptoglobin. Temperament score was assessed again on d 40 and d 200. Acclimated heifers had reduced (P = 0.01) concentrations of cortisol and haptoglobin on d 40 and reduced (P = 0.02) exit velocity on d 200 compared with control heifers. Puberty was hastened in acclimated heifers compared with control (P = 0.01). Results from this study indicate that B. taurus beef cows with aggressive temperament have impaired reproductive performance compared with cohorts with adequate temperament, whereas acclimation to human handling after weaning hastens reproductive development of replacement heifers.

Protein and glucogenic precursor supplementation: A nutritional strategy to increase reproductive and economic output1

Reproductive performance in young beef cows is often compromised due to a mismatch of physiological demands and suboptimal environmental conditions. Studies conducted at the Corona Range and Livestock Research Center from 2000 to 2007 evaluated 3 postpartum supplement strategies that varied in the amount of glucogenic potential (GP) supplied. Reproductive variables, milk production, and serum metabolites were used to assess supplement effectiveness and economics associated with 2- and 3-yr-old beef cows (n = 379) grazing native range. Supplements were individually fed twice/week at 1,135 g/d (2003 to 2004) or 908 g/d (all other years) and provided 1) 327 g of CP, 109 to 118 g of RUP (CON); 2) 327 to 341 g of CP, 142 to 157 g of RUP (RUP); or 3) 327 g of CP, 151 to 173 g of RUP + 40 to 100 g of propionate salt (PS; RUP+PS). Ultimately, total GP for CON, RUP, and RUP+PS was 44 to 47, 57 to 70, and 93 to 141 g, respectively. Blood samples were collected once/week (2000) or twice/week (2001 to 2007) for progesterone analysis to estimate days to resumption of estrus. Cows were exposed to bulls for 60 d or less, and pregnancy was confirmed by rectal palpation at weaning. Days to resumption of estrus after calving decreased linearly (P = 0.02), resulting in an increased pregnancy rate (P = 0.03) with increasing GP. Milk production exhibited a quadratic (P = 0.04) response to increasing GP, with cows fed RUP producing the most amount of milk. However, a linear decrease (P = 0.07) in days from BW nadir to estrus was found with increasing GP. Total kilograms of calf weaned per cow exposed for the supplemental year and subsequent year was increased linearly (P = 0.07) with increased GP. The improvement in pregnancy rate by supplementing RUP+PS resulted in an increase in total revenue of 18% compared with CON-fed cows and 9.5% compared with RUP-fed cows in the subsequent year after supplementation. These data suggest feeding young cows additional GP in the form of PS allows for partitioning of nutrients away from milk production and toward reproduction, allowing for increased profitability by increasing pregnancy rates and decreasing days to resumption of estrus.

The effect of increasing amount of glucogenic precursors on reproductive performance in young postpartum range cows1

Supplementing CP and propionate salts (PS) may improve economic returns in young range beef cows by increasing the dietary supply of glucogenic precursors. A 3-yr study conducted at Corona Range and Livestock Research Center (Corona, NM) from February to mid-July in 2005 (n = 80), 2006 (n = 81), and 2007 (n = 80) evaluated days to first estrus, calf weaning weight, BW change, and metabolic responses in 2- and 3-yr-old postpartum cows grazing native range. Cows were individually fed one of three 36% CP supplement treatments after parturition, with increasing glucogenic potential (GP) supplied by RUP and PS. Supplements were isoenergetic and fed at a rate of 908 g/cow per day twice weekly. Supplementation was initiated 7 d after calving and continued for an average of 95 d. Supplement treatments provided 1) 328 g of CP, 110 g of RUP and 0 g of PS (PS0); 2) 328 g of CP, 157 g of RUP, and 40 g of PS (PS40); or 3) 329 g of CP, 158 g of RUP, and 80 g of PS (PS80). Ultimately, PS0, PS40, and PS80 provided 44, 93, and 124 g of GP, respectively. Body weight was recorded weekly and serum was collected twice weekly for progesterone analysis to estimate days to first estrus. Cows were exposed to bulls for 60 d or less beginning in mid-May. Days to first estrus exhibited a quadratic (P = 0.06) response to GP resulting from the fewest days to first estrus with the consumption of PS40. Pregnancy rates were 88, 96, and 94% for cows fed PS0, PS40, and PS80, respectively (P = 0.11). Total kilograms of calf weaned per cow exposed to bulls for the supplementation and following year increased quadratically (P = 0.09). However, supplement did not affect milk composition or yield (P ≥ 0.53). Serum acetate half-life decreased linearly (P = 0.08) with increasing GP in 2007. Predicted margins were the greatest (quadratic; P = 0.03) for cows fed PS40. Even though supplement costs were greater for PS40 and PS80, cows fed PS40 had increased profits ($33.47/cow) compared with cows fed PS0 and PS80. This study implies that young postpartum cows fed additional glucogenic precursors may have improved reproductive efficiency and may wean more calf weight per cow exposed to breeding.

Effects of breed type and age at first calving on length of productive life in a cow–calf system in Southeastern Mexico

The effect of age at first calving (AFC) and breed type (BG) on cow length of productive life in the herd (LPL) and cumulative kilograms of calves weaned per cow (KWC) was studied. Data on 313 Brahman, 183 Nellore, and 269 crossbred cows (undefined crosses of European × Zebu cattle) born from 1986 to 2002 were used. Three hundred and ninety-one out of the 765 cows had non-censored data. LPL curves by BG and AFC (<2.5, 2.5 to <3, 3 to <3.5, and ≥ 3.5 years of age) were obtained using life table procedures. The magnitude of the effect of AFC and BG on LPL was determined using Cox proportional hazard regression procedures. KWC data (n=359) were analyzed by a linear model that included the effects of period of birth of the cow (in years), BG, and AFC. There was no difference in the survival curves between BG (p>0.05), but there was for the hazard ratio of culling (p<0.05). Brahman and Nellore cows produced more kilograms of calves (p<0.05) than crossbred cows. AFC influenced LPL (p=0.014) and KWC (p=0.012). Cows with AFC <3 years of age stayed longer in the herd and weaned more KWC than those with a higher AFC (p<0.05).

Forage systems for cow-calf production in the Appalachian region1

Small cow-calf operations are common in the Appalachian region. Tall fescue [Lolium arundinaceum (Schreb.) S. J. Darbyshire] is the dominant forage in these systems for direct grazing as well as for stockpiling. The present study was conducted from 2001 to 2005. A total of 108 Angus and Angus crossbred cows were allotted randomly to 6 forage systems and then to 3 replicates within each system. In brief, system 1 had a stocking rate of 0.91 ha/cow in a Middleburg 3-paddock (A, B, and C) system. System 2 was similar to system 1 except for a stocking rate of 0.71 ha/cow. A stocking rate of 0.71 ha/cow also was used in systems 3 through 6. All A paddocks had tall fescue, whereas B paddocks had tall fescue/white clover (Trifolium repens L.) except in system 6, which had tall fescue/lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don]. System 3 evaluated a 2-paddock (A and B) rotational grazing system, and system 4 evaluated a 3-paddock (A, B, and C) rotational grazing system, with paddock C containing orchardgrass (Dactylis glomerata L.) and alfalfa (Medicago sativa L.). Systems 5 and 6 differed from system 2 in the areas of paddocks B and C as well as in the forage mixtures used. In paddock C, system 5 had switchgrass (Panicum virgatum L.) and system 6 had tall fescue and birdsfoot trefoil (Lotus corniculatus L.). System 1 had the greatest average herbage availability from weaning until breeding (P < 0.05) with the least amount of hay fed (P = 0.03) when compared with the remainder of the systems. Differences (P > 0.05) in percentage of ground cover were not detected among systems. There was no year x system interaction effect on the cow or calf performance variables evaluated and no treatment effect on cow performance variables. There was a treatment effect on calf performance variables. System 2 produced the greatest adjusted weaning weight, kilograms of calf weaned per hectare, and kilograms of calf per kilograms of cow at weaning (P < 0.05). Numerical ranking for total calf production per hectare from the greatest to least was system 2, 6, 3, 5, 4, and 1. Systems evaluated did not affect cow performance although differences in calf performance and overall productivity of the systems were observed.

Calf Respiratory Disease and Pen Microenvironments in Naturally Ventilated Calf Barns in Winter

Relationships between air quality, a variety of environmental risk factors, and calf respiratory health were studied in 13 naturally ventilated calf barns during winter. A minimum of 12 preweaned calves were randomly selected and scored for the presence of respiratory disease in each barn. An air sampling device was used to determine airborne bacteria colony-forming units per cubic meter (cfu/m3) of air in calf pens and central alleys within the barns. Airborne bacteria samples were collected on sheep blood agar (BAP) and eosin methylene blue (EMB) agar plates. Temperature and relative humidity were recorded in each calf pen, the barn alley, and outside the barn. Samples of bedding were collected in each pen and DM was measured. Pen bedding type and a calf nesting score (degree to which the calves could nestle into the bedding) was assigned to each barn. Calf numbers, barn and pen dimensions, ridge, eave, and curtain openings, and exterior wind speed and direction were determined and used to estimate building ventilation rates. Factors that were significantly associated with a reduced prevalence of respiratory disease were reduced pen bacterial counts (log10 cfu/m3) on BAP, presence of a solid barrier between each calf pen, and increased ability to nest. Individual calf pen bacterial counts were significantly different from barn alley bacterial counts on both BAP and EMB. Significant factors associated with reduced calf pen bacterial counts on BAP were increasing pen area, increasing number of open planes of the calf pen, decreasing pen temperature, and wood-particle bedding. Significant factors associated with reduced alley bacterial counts on BAP were increased ventilation changes per hour, increased barn volume per kilogram of calf, reduced pen bacterial counts, and barn type.

Estimativas de parâmetros genéticos para características de crescimento e produtividade em vacas da raça Canchim, utilizando-se inferência bayesiana

O objetivo neste trabalho foi estimar as herdabilidades e as correlações genéticas dos pesos à desmama (PD), aos 12 meses de idade (P12) e à idade adulta (PAD), da idade de descarte (TPR - tempo de permanência no rebanho), do número (ND10) e quilogramas (QD10) de bezerros desmamados em até dez anos de idade, do número total (NDT) e quilogramas totais (QDT) de bezerros desmamados durante todo o tempo de permanência no rebanho e dos quilogramas de bezerros desmamados por ano de permanência no rebanho (QTPR) de fêmeas de um rebanho da raça Canchim. As estimativas dos componentes de (co)variância foram obtidas pelo método bayesiano, em análises bicaráter de PD, P12 e PAD com as demais características. Os modelos estatísticos incluíram os efeitos aleatórios genético aditivo direto, de ambiente permanente e residual e os efeitos fixos de ano e mês de nascimento ou do parto, da idade da vaca ao parto e da idade do animal, dependendo da característica. As médias das estimativas de herdabilidade foram iguais a 0,38 (PD), 0,40 (P12), 0,54 (PAD), 0,22 (TPR), 0,22 (ND10), 0,24 (QD10), 0,23 (NDT), 0,23 (QDT) e 0,32 (QTPR), indicando que as características possuem variação genética aditiva suficiente para boa resposta à seleção. As correlações genéticas entre TPR (-0,02; 0,26 e -0,12), ND10 (0,04; 0,10 e -0,29), QD10 (0,37; 0,39 e -0,13), NDT (-0,03; 0,14 e -0,25), QDT (0,20; 0,33 e -0,16) e QTPR (0,21; 0,28 e -0,19) e os pesos (PD, P12 e PAD), ao contrário do aumento do peso adulto, sugerem que a seleção de fêmeas com base nos pesos à desmama e aos 12 meses de idade não deve prejudicar as características de longevidade e de produtividade estudadas.

Effect of copper, zinc, and manganese supplementation and source on reproduction, mineral status, and performance in grazing beef cattle over a two-year period.

Crossbred, multiparous beef cows (n = 178 in Year 1; n = 148 in Year 2) were used to evaluate the effects of Cu, Zn, and Mn supplementation and source on reproduction, mineral status, and performance in grazing cattle in eastern Colorado over a 2-yr period. Cows were stratified by expected calving date, age, BW, BCS, and liver mineral status and assigned to the following treatments: 1) control (no supplemental Cu, Zn, or Mn); 2) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn); and 3) inorganic (ING; 100% inorganic CuSO4, ZnSO4, and MnSO4). Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Zn, and Mn from 82 d (Year 1) and 81 d (Year 2) before the average calving date of the herd through 110 d (Year 1) and 135 d (Year 2) after calving. At the end of Year 1, supplemented cows had greater liver Cu (P < 0.01), Zn (P < 0.05), and Mn (P < 0.01) concentrations compared with controls, whereas liver Cu concentration was greater (P < 0.01) in ORG vs. ING cows. At the end of Year 2, supplemented cows had greater (P < 0.01) liver Cu concentrations relative to controls, whereas control cows had greater (P < 0.02) liver Mn concentration than did supplemented cows. In Year 1, pregnancy rate to AI in control cows did not differ (P = 0.47) from supplemented cows, but there was a trend (P < 0.08) for pregnancy rate to be higher for ORG than ING cows. In Year 2, supplemented cows had a higher (P < 0.02) pregnancy rate to AI than controls. In both years, when cows were inseminated after an observed estrus, supplemented cows had a higher (P < 0.04) pregnancy rate than did controls. Also, for both years, overall 60-d pregnancy rate tended (P = 0.10) to be higher for supplemented cows than for controls. In Year 1, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and kilograms of calf weaned per cow exposed was greater (P < 0.01) in ING than ORG treatments. However, in Year 2, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and tended (P = 0.09) to be greater in ORG than ING treatments. Results indicate that supplementation and source of trace minerals affected mineral status and kilograms of calf weaned per cow exposed in grazing beef cows. Supplementation also improved pregnancy rate to AI compared with cows not supplemented with Cu, Zn, or Mn for more than 1 yr. Furthermore, mineral source may influence pregnancy rate to AI.