Cow breeding and calf growth performance as affected by pregnancy status the previous year

A 2-yr study was conducted to compare the subsequent cow breeding and calf performance of cows that were nonpregnant with cows that were pregnant at the time calves were weaned. Cows were Angus (A), Polled Hereford (PH), Santa Gertrudis (SG) straightbreds and crossbreds of these breeds. Nonpregnant cows (G1) were 4- to 9-yr-olds that had a calf the previous year and appeared to be physically sound with no detection (by rectal palpation) of an abnormal reproductive tract due to disease, abnormal growth or calving difficulties. Pregnant cows (G2) were of similar age and breed composition to G1 cows. The 93 G1 and the 193 G2 cows were assigned within age and breed composition to sire breeding groups on pasture in an approximate 1:2 ratio, respectively, per sire. There were six A, three PH and one SG sires. The year prior to G1 cows being nonpregnant, G1 cows calved 11 d later (P less than .01) than G2 cows. Subsequent to their being nonpregnant, G1 cows gained 27 kg more (P less than .001) weight during the breeding period, had 5.4 percentage units more (P less than .29) calves born, had calves 17 d earlier (P less than .001) in the calving period, had calves that gained at a similar rate to weaning and had calves that were 14 kg heavier (P less than .01) at weaning (due to their being 17 d older) compared with G2 cows and calves.     

Breeding performance of bulls assigned either to 40 cows per bull or 80 cows per two bulls during the breeding period

The reproductive performance of Angus (A), Polled Hereford (PH) and Santa Gertrudis (SG) bulls was compared when exposed to 40 cows/bull vs 80 cows/two bulls during a 90- to 95-d breeding period on pasture. Cows were A, PH and SG straightbreds and crossbreds of these breeds. Each year, cows were allotted at random within breed composition and age of dam to breeding groups. A replicate consisted of two 40-cow single-sire units with bulls of two breeds and an 80-cow two-sire unit with two bulls of the same breeds and all four bulls of the same age. There were eight replicates of PH and SG bulls and five replicates of PH and A bulls. At breeding time, 20, 16, 12 and 4 bulls were 2-, 3-, 4- and 5-yr-olds, respectively. Reproductive performance of bulls was evaluated in terms of calving rate (CR) of cows exposed to them and number of days (NOD) from the beginning of the breeding period until calf birth. The 80-cow groups calved 3.7 d earlier (P less than .05) in the calving period and had a similar CR compared with the 40-cow groups. The PH-A replicates calved 3.5 d earlier (P less than .05) and had 7.3 percentage units higher (P less than .01) CR than PH-SG replicates. Results of this study indicated that 80-cow two-sire breeding groups had an advantage over the 40-cow single-sire groups in terms of calves born earlier in the calving period, with no reduction in CR.     

Effects of breeding season length and calving season on range beef cow productivity

A 5-yr study was conducted beginning in 1983 with 460 cows to evaluate the effects of three breeding seasons (30, 45, and 70 d in length) and two times of spring calving, March (early) and April (late), on cattle production under Nebraska Sandhills range conditions. Criteria evaluated included pregnancy and weaning percentages, calving date and distribution, cow weights and body condition at four intervals, calf birth and weaning weights, and cow productivity. The 30-d breeding season included a 10-d estrus synchronization and AI period; in the other breeding seasons only natural breeding was used. The same sires were used over the entire study period. Percentage of cows pregnant and percentage of calves weaned were lower (P less than .01) for cows bred for 30 d than for cows bred for 45 or 70 d. Average calving dates were similar among the breeding groups within the early and late calving herds. Pregnancy rates from AI were higher (P less than .01) for the cows calving in April (64%) than for the cows calving in March (41%). Cows calving in April lost less weight between precalving and prebreeding and were heavier (P less than .05) at prebreeding time than the cows calving in March. Calf weaning weights were not different (P greater than .10) among any of the breeding season groups or between the two calving herds when calves were weaned at a similar age. Cow productivity (calf weaning weight per breeding female) was highest (P less than .05) for the cows bred for 70 d (186 kg), intermediate for the cows bred for 45 d (172 kg), and lowest for cows bred for 30 d (162 kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of crossbred cows containing various proportions of Brahman in spring or fall calving systems: III. Productivity as three-, four-, and five-year olds

Productivity of 3-, 4-, and 5-yr-old crossbred cows containing various proportions (0, 1/4, or 1/2) of Brahman breeding out of Angus or Hereford dams was evaluated using 489 spring-calving and 427 fall-calving records collected over a 4-yr period. Cows were bred to Limousin sires for the first 3 yr and to Limousin and Salers sires the 4th yr. Interactions between crossbred cow group and season of calving were not significant. Percentage of cows exposed to breeding that weaned a calf increased (P less than .01) as proportion Brahman breeding increased, was higher (P less than .01) for cows out of Angus dams than for cows out of Hereford dams, and was higher (P less than .01) for spring-calving cows. As the proportion Brahman increased, the percentage requiring assistance at birth decreased, and cows out of Angus dams required less (P less than .05) assistance than those out of Hereford dams. Preweaning ADG, adjusted weaning weight, weaning conformation, weaning condition, and adjusted weaning hip height increased a proportion Brahman breeding increased. Spring-born calves gained .12 kg/d faster (P less than .01) than fall-born calves. However, weight at weaning was similar for the two groups; spring-born calves were weaned at an average age of 205 d, and fall-born calves were weaned at an average age of 240 d. Fall-calving cows were heavier (P less than .05) than spring-calving cows, and 0 and 1/2 Brahman cows were heavier (P less than .01) than 1/4 Brahman cows. These data indicate that Brahman-cross dams can be used to improve reproductive rate and increase preweaning growth rate, and thus weaning weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production characters of first-generation cows of a five-breed diallel: reproduction of young cows and preweaning performance of inter se calves

Data from cows of a five-breed diallel involving Angus, Brahman, Hereford, Holstein and Jersey were analyzed. Females were used in inter se matings to produce three second-generation parturitions per cow. Crossbred (CB) cows were 43 d younger (P less than .05), 14 kg heavier (P less than .05) and 2 cm taller (P less than .05) at first calving than straightbred (SB) cows; however, no differences were detected (P greater than .10) between the two groups for pelvic measurements. Although large differences among breed types existed for gestation length, crossbreds generally did not differ from straightbreds for this character. Crossbred cows exhibited a 7.5 d shorter (P less than .05) interval from parturition to first service, but did not exhibit a shorter interval from parturition to conception (P greater than .10). The dairy breeds (Holstein and Jersey) and their crosses exhibited similar postpartum and calving intervals as Angus, while Brahman and their crosses had longer intervals. Crossbred calves were 1.3 kg heavier (P less than .01) and had greater (P less than .01) shoulder and hip dimensions at birth than SB calves, but no difference in the amount of calving difficulty was detected (P greater than .10) between the two groups. Higher (P less than .01) rates of survival to 24 h (3.7%) and to weaning (8.7%) were observed for CB calves compared with SB calves. Heterotic effects for weaning weight (15.2 kg), weaning height (2 cm) and preweaning average daily gain (68 g) were large and illustrate the importance of individual and maternal heterosis for these characters. These results suggest that substantial amounts of heterosis may be retained for survival and weaning characters of calves in early generations of inter se mating of CB.     

Lifetime production of beef heifers calving first at two vs three years of age

Records of Angus, Hereford, Shorthorn, and first-cross cows born from 1960 to 1963 were used to study the effect of age at first calving and culling policy on cumulative survival (SU), number of breeding seasons (BS), pregnancies (PG), calves born (CB) and alive at 72 h (C72) and at weaning (CW), calf weaning weights (WW), and input/output efficiency, up to 12 yr of age. The 155 cows born in 1960 and 1961 calved first at 3 yr of age (M3) and the 173 born in 1962 and 1963 calved at 2 yr of age (M2). Analyses included both actual culling of cows open in two consecutive years (AC) and imposed culling of any open cow (IC). Also, economic efficiency for no culling (NC) of cows for infertility after first calving and up to 10 yr of age was calculated. The model included cow birth year-sire breed of cow (Y-S), sires within Y-S, breed of cow's dam (D), and D x Y-S. Linear functions of Y-S were used to estimate means for M2 and M3 cows. Under AC, by 12 yr of age M2 exceeded M3 cows by 6.8% SU, 1.1 BS, 1.2 PG, 1.1 CB, 1.0 C72, .9 CW, and 138 kg WW (P less than .10). Under IC, M2 exceeded M3 cows by only .7% SU, .3 BS, .3 PG, .3 CB, .2 C72, and .1 CW; and M3 produced 24 kg more WW than M2 cows (P greater than .10). Economic efficiency was higher for M2 than for M3 cows (greater than 10% at 6 yr to greater than 5% at 12 yr culling age), regardless of culling policy. Economic efficiency was maximum when terminal age of cows was 6 to 9 yr for M2 and 8 to 9 yr for M3 cows. Repeatability of pregnancy was higher (P less than .05) for M3 (19%) than for M2 (2%) cows. Economic efficiency for M2 or M3 cows under NC was slightly poorer (2 to 3%) than under either AC or IC policies. Economic efficiency can be improved by managing heifers to calve first as 2-yr-olds under either mild or intense culling of open cows.     

Comparison of crossbred cows containing various proportions of Brahman in spring- or fall-calving systems: IV. Effects of genotype x environment interaction on lifetime productivity of young cows.

Lifetime productivity of young (2 to 6-yr-old) crossbred cows containing various proportions (0, 1/4, or 1/2) of Braham breeding was evaluated using 188 spring-calving and 154 fall-calving cows. Cows were mated to Limousin sires to produce 1983 through 1986 calf crops. The 1987 calf crops were produced using Limousin and Salers sires. Significant (P less than .10) genotype (crossbred cow group) x environment (season of calving) interactions were found for age at first calf and lifetime calving percentage and mature cow weight. Within the spring calving group, no differences were found between crossbred groups for age at first calf or lifetime calving percentage. However, within the fall-calving group, 0 and 1/2 Braham cows from Angus dams calved earlier than did those from Hereford dams. Age at first calf also tended to increase as proportion of Brahman increased in the fall-calving group. Within the fall-calving group, lifetime calving percentage for 0 and 1/2 Brahman cows from Hereford dams was lower than for those from Angus dams. The opposite was true for the 1/4 Braham crosses. In general, as the proportion of Brahman breeding increased, productivity, measured as weight per calf or weight weaned per year, increased; however, age at first calving increased also as proportion of Brahman increased. All spring-calving groups calved earlier in life (P less than .05) than their respective fall-calving counterparts and with the exception of the 0 Brahman groups, which were similar, spring-calving groups produced a higher (P less than .05) percentage of calves than did the fall groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Reproductive performance and variation in body weight during annual cycles for crossbred beef cows with different genetic potential for milk

Reproductive performance and body weights were studied in 81, 79 and 88 spring-calving beef cows from three groups, reasonably similar in growth rate and mature size but different in level of milk production (low [L] = Hereford x Angus, medium [M] = Red Poll x Angus and high [H] = Milking Shorthorn x Angus). Milk group did not have a significant effect on dates of first postpartum estrus and first and last breeding or in the intervals from calving to first estrus, to first breeding and to last breeding. A significant age-of-cow x milk-group interaction was found for pregnancy rate (PR, P less than .10) and calf-crop percentage (CC, P less than .05). In heifers, PR and CC were lowest for the L (85.6 and 73.6%) and highest for the M group (94.2 and 92.5%); in 2-yr-olds there were no differences, and in older cows, PR was highest for the L (94.8%) and lowest for the H group (91.6%), and there were no differences in CC. As estimated from Brody's growth curves, mature sizes were 530 +/- 5.7, 471 +/- 4.6 and 499 +/- 4.2 kg for the L, M and H groups, respectively. Of weights taken on four occasions during the year, October weight was the highest for all cows. February weight, minus the estimated gravid uterus weight, was the lowest for L and M cows, and May weight was lowest for H cows. Weight fluctuation over an annual cycle was greatest for the L group. Under these experimental conditions, cows in all groups were able to consume sufficient energy and gain or lose body reserves to achieve similar reproductive performance while differing in lactation performance.     

Size and management effects on reproduction in first-, second- and third-parity beef cows

The effects of size, management and size x management interactions on reproduction in beef cattle were determined by using 3,126 breeding and calving records from 1980 to 1985. Cows were from three synthetic lines that differed in mature size (small, medium and large). The lines differed also in the percentages of Jersey, Angus and Simmental. Each line was replicated in two herds. One herd (Rhodes) followed a spring calving schedule and weaned calves at about 180 d of age. The other herd (McNay) calved cows in the fall and weaned calves early at about 45 d of age. Cycling rate, conception rate, abortion rate and calving rate were each evaluated for first-, second- and third-parity dams. An important interaction (P less than .05) was found between lines and management in heifers. Cycling rate and calving percentage were almost identical for all three lines in the Rhodes herd, but small heifers in the McNay herd had about 20% higher cycling (83.8 vs 63.1%) and calving rates (73.8 vs 53.0%) than large heifers. Line x management interactions were not significant in second- and third-parity dams, but line did remain a significant source of variation in calving rate. Calving rates in second-parity dams were 85.0, 78.1 and 70.7% for small, medium and large cows, respectively. In third-parity dams, small cows had a higher calving rate (P less than .05) than either medium or large cows (80.9 vs 66.1 or 68.7%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in pelvic conformation and peripheral estrone concentrations in pre- and post-partum beef cows

An experiment was conducted to investigate the temporal relationship of peripheral estrone (E1) concentration to changes in the size of the pelvic opening preceding and immediately following parturition. Twenty-six multiparous beef cows were observed from approximately 50 d prepartum to 7 d postpartum. Blood samples were collected at 7 d intervals preceding calving and at 1, 3 and 7 d following for E1 quantitation. Estimates of pelvic opening area were made at the time of blood sampling. Peripheral E1 concentrations were elevated beginning at approximately 25 d prepartum. Dams bearing male fetuses had greater (P less than 0.01) concentrations of E1 than did dams with female fetuses. Calf birth weight was correlated (r = 0.44, P less than 0.01) with E1 levels from 10 d prepartum through parturition. Postpartum pelvic area was greater for cows giving birth to male calves, with no significant differences for calf birth weights by sex. Correlations were observed between E1 concentration, and pelvic area measured from 50 d prepartum to 7 d postpartum (r = 0.26, P less than 0.01), 10 d prepartum to calving (r = 0.42, P less than 0.01), and from calving to 7 d postpartum (r = 0.33, P less than 0.01). Percentage increase in E1 concentration from 50 d prepartum to calving was significantly correlated (r = 0.75, P less than 0.01) to percentage pelvic area increase over the same period. A correlation also exists between maternal E1 concentrations and fetal sex and pelvic area. In summary, the increased estrogen concentrations in cows with male calves may facilitate pelvic spread, resulting in a larger pelvic opening.     

Performance, blood and ruminal characteristics of cows receiving monensin and a magnesium supplement

Forty-eight Angus and Hereford cows were used in a completely random design with a 2 X 2 factorial arrangement of treatments to evaluate the effects of monensin and two sources of Mg on performance, ruminal characteristics and mineral status of mature beef cows. Cows were fed wheat straw treated with NH3 during late gestation and straw treated with NH3 plus bromegrass haylage after calving along with a protein supplement that contained either MgO (7.5 g/kg) or MgSO4 (11 g/kg). One half of the cows received monensin (1 g/kg) in their protein supplement. During the precalving period, MgO without monensin increased (P less than .01) plasma Mg compared with Mg in plasma of cows receiving MgSO4 or MgO with monensin. Magnesium oxide also increased cow weight gains during late gestation (P less than .05) compared with weight gains of cows supplemented with MgSO4, but magnesium source had no effect on weight gain postcalving. Plasma glucose was increased by monensin (P less than .05) and by MgSO4 (P less than .01) during early lactation. Monensin increased the proportion of propionate before (P less than .05) and after (P less than .10) calving in the ruminal fluid of cows. Monensin also increased (P less than .05) cow weight gain precalving and tended to decrease (P less than .10) milk fat in lactating cows. Calf weight gains were not affected by treatment of dam. Magnesium oxide appeared to have higher Mg bioavailability than MgSO4 for cows precalving, but Mg bioavailability was not different postcalving. Monensin increased cow weight gains precalving and improved feed efficiency postcalving.     

Effect of calf weaning age and cow supplementation on cow productivity

Five years of data were collected on 124 Brangus-type cows to evaluate weaning calves at 8.5 or 10.5 mo of age and winter supplementation of the brood cow with 2.25 kg of molasses daily. Cows with calves weaned at 10.5 mg of age gained 14 kg less weight (P less than .01) during the late nursing period than did cows from which calves were earlier weaned. Age of calf at weaning had no effect on cow reproduction, but calves weaned at 10.5 mo were 2 to 3 d younger (P less than .06) and 5.3 kg lighter (P less than .05) at 8.5 mo of age. During the last 2 mo of nursing, calves weaned at 10.5 mo of age gained 37.2 kg and had a 31.9-kg heavier weaning weight than calves weaned at 8.5 mo of age. Molasses supplementation resulted in differences (P less than .01) in cow weight changes. Cows fed molasses had calving percentages 5 to 7 units higher (P less than .30) than cows not fed molasses. Feeding cows molasses for 145 d throughout the calving and breeding season increased calf weaning weight 7.7 (P less than .02) and 11.2 (P less than .03) kg, respectively, at 8.5 and 10.5 mo of age over the nonsupplemented controls.     

Response of postpartum beef cows to exogenous progestogens and gonadotropin releasing hormone

Plasma progesterone (P4) profile and estrous detection were used during three experiments to evaluate the effects of exogenous progestogens on the life span of gonadotropin releasing hormone (GnRH)-induced corpora lutea (CL) in postpartum (pp) beef cows. Experiment 1 utilized primiparous fall-calving cows (n = 28, trial 1); and spring-calving cows (n = 29, trial 2). On d 18 to 27 pp (d 0) all cows received intravaginal devices containing either P4 or no P4 (NP) for 5 d. On d 5 the devices were removed and calves were either removed (CR) or were present (CP) with half of the cows within steroid group. At 50 h after device removal, 500 micrograms of GnRH was given (iv) to all cows, and weaned calves were reunited with their dams. The induced CL had a normal life span (greater than 16 d) in 17 and 86% (trial 1) and 8 and 79% (trial 2) of NP and P4 cows, respectively. Calf removal did not affect (P greater than .10) the life span of the CL. In Exp. 2, spring-calving multiparous cows (d 18 to 24 pp; d 0) received either no P4 (NP; n = 19), P4 for 6 d via intravaginal devices (P4H; n = 19) or a single im injection of 300 mg P4 (P4 IM; n = 18). At 48 h after device removal or at 8 d after the injection of P4, half of the cows within steroid group received either 500 micrograms GnRH or saline. Corpora lutea had a normal life span in 0, 11, and 80% of NP, P4 IM and P4H cows, respectively, that received GnRH and in 22% of P4-saline cows. In Exp. 3, fall-calving multiparous and primiparous cows (d 25 to 31 pp) received either no progestogen (NP; n = 20), P4 via intravaginal devices for 5 d (P4H; n = 21) or melengestrol acetate (MGA; .5 mg.head-1.d-1 for 5 d orally, n = 15). At 48 d after device removal or at 72 h after the last MGA feeding, all cows received 500 micrograms GnRH. Progesterone post-GnRH injection was increased (greater than 1 ng/ml) at d 7 in 64, 100 and 100%, and remained elevated at d 14 in 11, 46 and 100% of NP, MGA and P4H cows, respectively. For all experiments plasma P4 was increased (range 2 to 5 ng/ml) when the devices containing P4 were in place, then decreased (less than 1 ng/ml) by 48 to 50 h after device removal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Productivity of different cow genotypes: culling rates and early calf performance

Records of Jersey-sired (Jx), Santa Gertrudis-sired (Sx), Charolais-sired (Cx) and straightbred Hereford (H) cows were examined to determine culling rates, birth dates, weaning weights and average daily gains of their first, second and third calves. Culling categories were defined on the basis of number of calves weaned before removal from the herd. Calf performance data were analyzed by cow breed group and cow culling category. A second-degree polynomial model fit the data of all breeds, and accounted for a greater proportion of variation in percentage culled than did the linear model (P less than .05). Total percentage culled through the study were 71, 67, 54 and 53 for the H, Sx, Cx and Jx cows, respectively. Culling rates in the H and Sx cows tended to be higher at earlier ages than in the Cx and Jx cows. Cow-culling category was a significant source of variation only on birth date of first calves. Cows culled after one calf had calves that were born later than cows in the other two categories (P less than .05). Birth date, weaning weight and average daily gain of first calves varied with cow breed in that Jx cows had calves that were born earlier, gained faster and weaned heavier than first calves from the other breed groups (P less than .05). First calves from Sx and Cx cows gained faster (P less than .05) than calves from H cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Output/input differences among nonpregnant, lactating Bos indicus-Bos taurus and Bos taurus-Bos taurus F1 cross cows

Nonpregnant F1 crossbred cows, progeny of either Hereford (H) or Angus (A) dams and sired by Brahman (Bm), Sahiwal (Sw), Pinzgauer (Pz), H, or A sires, were fed to maintain initial weight while rearing Charolais (C)-sired progeny for a period of 126 d in drylot commencing at about 48 d postpartum. Cow-calf pairs were assigned to equalize cow age, calf sex, and breed of cow's dam among three replicate pens of approximately 12 pairs each. Cows and calves were weighed every 2 wk and feed intake was adjusted to minimize change in cow weight. Metabolizable energy (ME) consumption for zero cow weight change was estimated by regression. Milk production was estimated by weight-suckle-weigh at 58, 85, 125, and 170 d of lactation. Calf gain (GAIN, kg) relative to cow weight (CWT1, kg) was higher (P less than .01) for calves from Bm-X (139.5/585) and Sw-X (132.2/534) than for calves from Pz-X (127.2/552) and HA-X (116.9/547) cows. Estimated mean daily production of milk was 7.40, 7.15, 7.28, and 6.37 kg for the Bm-X, Sw-X, Pz-X, and HA-X, respectively. Total cow ME intake (TMEcow) for breed groups ranked (P less than .05) with cow size and milk production, and calf creep-feed intake (FMEcalf) was inversely related to estimated milk intake. Proportion of total feed ME (TMEcow+calf) consumed by calves was higher (P less than .05) for HA-X cows (18%) than for the others (14%). Total efficiency of calf gain in weight (GAIN/TMEcow+calf) was 11% greater (P less than .05) for crossbred cows of Bos indicus X Bos taurus (Bm-X, Sw-X) than for Bos taurus X Bos taurus (Pz-X, HA-X) cows (35 vs 32 g/Mcal) in the 126-d lactation period.     

Genotype x environment interactions involving proportion of Brahman breeding and season of birth. I. Calf growth to weaning

Performance to weaning was evaluated on 489 spring-born and 416 fall-born crossbred calves of three proportions of Brahman breeding (0, 1/4 and 1/2 Brahman) over a 3-yr period. The calves were produced by appropriate matings of Angus (A), Hereford (H), Brahman (B), 1/2B-1/2A and 1/2B-1/2H bulls to Angus and Hereford cows. Interactions between proportion of Brahman breeding and season of birth existed (P less than .01) for all traits except birth weight. Birth weights of 1/4 and 1/2 Brahman calves were 1.4 and 3.8 kg heavier (P less than .05), respectively, than 0 Brahman calves. Spring-born calves that were 1/4 and 1/2 Brahman outgained (P less than .05) 0 Brahman calves 36 and 69 g/d, respectively, and were 9 and 18 kg, respectively, heavier (P less than .05) at weaning, whereas preweaning average daily gains and weaning weights were similar among fall-born cross-bred calf groups. Among spring-born calves, 1/4 and 1/2 Brahman calves were 2.6 and 6.6 cm, respectively, taller (P less than .05) than 0 Brahman calves, whereas among fall-born calves 0 and 1/4 Brahman calves had similar hip heights and 1/2 Brahman calves were 3.7 and 2.8 cm taller (P less than .05) than 0 and 1/4 Brahman calves, respectively. Conformation and condition scores were similar for crossbred groups among spring-born calves, whereas conformation and condition scores decreased as proportion of Brahman breeding increased among fall-born calves. These data indicated that genotype X environment interactions are important in beef production and increased proportions of Brahman breeding were advantageous in a spring-calving program but not in a fall-calving program.     

Effects of age on body condition and production parameters of multiparous beef cows

Pregnancy rate, calving interval, birth weight, weaning weight, and quarterly BCS were collected for 5 consecutive years on 454 fall-calving multiparous British crossbred cattle (3 to 10 yr of age) to evaluate associations of age with BCS and production parameters. Body weight and BCS were collected pre-calving, prebreeding, at weaning, and midway through the second trimester of pregnancy (August). Body condition score was correlated with age during all seasons (P < 0.01). At calving, breeding, and in August, 3-yr-old cows had the lowest BW and BCS, whereas 8-yr-old cows had the greatest. At weaning, these values were maximal in 10-yr-old cows. Pregnancy rate was near 80% up to 9 yr of age but decreased to 57% in 10-yr-old cows. The relationship of pregnancy rate with age appears to be correlated with the BCS decrease at breeding in the older cows, supported by the fact that inclusion of BCS at breeding in the statistical model eliminated the effect of age on pregnancy rate (P = 0.42). Calving interval was longer in 3-yr-old cows compared with 4- to 9-yr-old cows (P = 0.02); however, among older cows, there was little change in the calving interval. Birth weight reached a maximum at 8 yr of age (35 +/- 0.9 kg) and a minimum in 3-yr-old cows (32 +/- 0.7 kg). Birth weights of calves born to both 3- and 4-yr-old cows were lower than for those born to 5-, 6-, 7-, or 8-yr-old cows (P < 0.05). Ten-year-old cows weaned lighter calves (205-d adjusted weaning weight) than younger dams. Furthermore, 3-yr-old cows weaned calves 9 +/- 2.1 and 14 +/- 2.4 kg lighter than 4- and 5-yr-old cows, respectively (P < 0.001). Interpretation of the age analyses of calving interval, birth weight, and weaning weight was independent of the inclusion of BCS in the model. This study documents the effects of age on calving interval, birth weight, and weaning weight that are independent of BCS.     

Reproductive performance of Gyr cows: the effect of weaning age of calves and postpartum energy intake

Two nutritional levels following parturition and five weaning ages for the calf were evaluated to study their effect of reproduction in Gyr cows in the savannas of West Central Brazil (Campos Cerrados). Early weaning of calves reduced postpartum weight losses and shortened the postpartum interval to conception. Energy level did not affect cow weight at weaning or conception, the number of days from parturition to first estrus or the number of matings/conception; however, the postpartum period to conception was reduced (116 vs 160 d; P less than .05) for cows on the higher energy diet. Weaning age significantly affected postpartum weight loss in cows. Six months after calving, cows that nursed calves for 1 mo were 89 kg heavier than those that nursed calves for 6 mo (384 vs 295 kg; P less than .05). Cows that were nursed for 1 mo returned to estrus at an average of 40 d postpartum, which was 23 d earlier (P less than .05) than the average of the other groups nursed for longer periods of time. There was no significant difference in the postpartum period to conception among cows that had their calves weaned at 1 mo, 3 mo and cows which were nursed twice daily beginning 30 d after parturition (57, 94 and 97 d, respectively), but was less (P less than .05) for cows nursed for 5 or 6 mo (212 and 231 d, respectively). The results show that Gyr cattle are genetically capable of responding reproductively to improve nutrition and reduced lactation stress achieved through early weaning or controlled nursing.     

Effects of inorganic and organic copper supplemented to first-calf cows on cow reproduction and calf health and performance

Two experiments were conducted to determine whether the supplementation of Cu in the organic or inorganic form to 2-yr-old cows, before and after calving, affects reproduction rate, calf health and performance, passive transfer of immunoglobulin, or liver and serum Cu concentrations compared with unsupplemented controls. Cows (n = 75 in 1997; n = 120 in 1998) were randomly assigned by estimated calving date and body condition score to one of three treatments: 1) Control, control; 2) Inorganic, inorganic Cu supplement (200 mg Cu from CuSO4); 3) Organic, organic Cu supplement (100 mg Cu from AvailaCu). In 1998, a fourth treatment was added; 4) CU-ZN, organic Cu and Zn (400 mg Zn from AvailaZn in the Organic diet). Cows were fed a hay-based diet and individually fed supplements for approximately 45 d before and 60 d after calving (approximately January 15 to May 15 each year). Liver biopsies were obtained from cows before supplementation began, and from cows and calves at 10 and 30 d after calving. Blood samples were obtained from both cows and calves at calving, and colostrum samples were collected for IgG and mineral content. Cow liver Cu concentrations before supplementation began were 58 mg/kg in 1997 and 40 mg/kg (DM basis) in 1998. By 10 d after calving, liver Cu concentrations of Control cows had decreased (P < 0.05) to 24 mg/kg (Cu deficient) in both years, whereas liver Cu concentrations of Cu-supplemented cows increased (P < 0.05) in both years. Calf liver Cu concentrations at 10 d of age were similar (P > 0.10) for all treatment groups. No differences (P > 0.10) were found in colostrum Cu concentrations, or in calf health among treatments. No differences (P > 0.10) were found in cow BW change, calf serum Cu concentrations, calf weaning weights, or in cow 60-d pregnancy rates among treatments in either year. In 1998, cows in the Organic group had higher (P < 0.05) 30-d pregnancy rate than Control cows. Neither serum samples nor placental tissue were reliable indicators of Cu status in cows. Feeding supplemental Cu (either inorganic, organic, or organic with extra Zn) to cows with liver Cu concentrations of approximately 50 mg/kg before calving did not improve cow 60-d pregnancy rates or the health and performance of their calves when compared with unsupplemented cows.