Cow Weight Change Research Articles

A review of factors influencing key biological components of maternal productivity in temperate beef cattle

Cow–calf efficiency or maternal productivity is highly correlated with total system efficiency of beef production. Balancing the needs of the cow herd with other production components is a daily challenge beef producers address to maximise the number of calves born and raised to weaning and, in turn, maximise maternal productivity. Pressure to satisfy modern consumer needs has shifted selection emphasis to production traits at the expense of fitness traits allowing adaptability to decline. Balancing the needs of the cow herd with production objectives presents cow–calf producers with the challenge of genetically tailoring their cattle to modern needs, while sustainably managing these cattle and natural resources. This balancing act is highlighted by the debate surrounding the application of residual feed intake to reduce costs associated with provision of feed for beef production. Some uncertainty surrounds the relationships between efficiency, production and maternal productivity traits. This review examines key components and definitions of maternal productivity. Management decisions as well as cow and calf traits have important interacting impacts on maternal productivity. Achieving a calving interval of 365 days represents the single most important production issue affecting maternal productivity and is dependent on heifer development during early life and energy reserves (i.e. body condition score) in subsequent years. Management issues such as calving date and selection decisions interact with environmental factors such as photoperiod and production traits such as feed intake, and previous production levels, to influence heifer development and cow body energy reserves. Some proposed definitions of maternal productivity simply include weaning weight per cow mated which can be averaged over all progeny weaned during a cow’s lifetime. Ideally, a definition should include the inputs and outputs of maternal productivity. Some definitions express maternal productivity over large time scales, e.g. a cow’s productive lifetime. Most definitions focus on the cow–calf unit, while some include progeny growth and feed intake to slaughter. This review recommends a definition that focuses on the cow–calf unit, as follows: (weight of calf weaned and cow weight change)/(metabolisable energy intake per cow and calf unit). This definition has the capacity to be scaled up, to include progeny postweaning production, as well as being applicable over varying time scales (e.g. 1 year to a cow’s whole productive life). Improvements in all facets of maternal productivity using this definition can be expected to improve beef-production efficiency.

Heterosis and direct effects for Charolais-sired calf weight and growth, cow weight and weight change, and ratios of cow and calf weights and weight changes across warm season lactation in Romosinuano, Angus, and F cows in Arkansas.

The use of Brahman in cow-calf production offers some adaptation to the harsh characteristics of endophyte-infected tall fescue. Criollo breeds, such as the Romosinuano, may have similar adaptation. The objectives were to estimate genetic effects in Romosinuano, Angus, and crossbred cows for their weights, weights of their calves, and ratios (calf weight:cow weight and cow weight change:calf weight gain) across lactation and to assess the influence of forage on traits and estimates. Cows ( = 91) were bred to Charolais bulls after their second parity. Calves ( = 214) were born from 2006 to 2009. Cows and calves were weighed in early (April and June), mid- (July), and late lactation (August and October). Animal was a random effect in analyses of calf data; sire was random in analyses of cow records and ratios. Fixed effects investigated included calf age, calf sex, cow age-year combinations, sire breed of cow, dam breed of cow, and interactions. Subsequent analyses evaluated the effect of forage grazed: endophyte-free or endophyte-infected tall fescue. Estimates of maternal heterosis for calf weight ranged from 9.3 ± 4.3 to 15.4 ± 5.7 kg from mid-lactation through weaning ( < 0.05). Romosinuano direct effects (of the cow) were -6.8 ± 3.0 and -8.9 ± 4.2 kg for weights recorded in April and June. Calf weights and weight gains from birth were greater ( < 0.05) for calves of cows grazing endophyte-free tall fescue except in mid-summer. Cow weight change from April to each time was negative for Angus cows and lower ( < 0.05) than other groups. Cows grazing endophyte-free tall fescue were heavier ( < 0.05) at all times but had more weight loss in late lactation. Angus cows had the lowest ( < 0.05) ratios (negative) of cow weight change:calf weight gain, indicating an energy-deficit condition. Cows grazing endophyte-free tall fescue had more negative ( < 0.05) values for this trait but not in early lactation ( < 0.05). Estimates of heterosis ranged from 12.8 ± 9.5 to 28.6 ± 9.4 kg for cow weight, 7.9 ± 3.0 to 15.8 ± 5.0 kg for cow weight change, and 0.07 ± 0.03 to 0.27 ± 0.1 for cow weight change:calf weight gain. Direct Romosinuano effects ranged from 14.8 ± 4.2 to 49.8 ± 7.7 kg for cow weight change and 0.2 ± 0.04 to 0.51 ± 0.14 for cow weight change:calf weight gain. The adaptive ability of Romosinuano in temperate fescue regions may be favorable with respect to relative cow and calf weight but may be a consequence of lower milk-producing ability.

Effects of supplementation on intake, digestion, and performance of beef cattle consuming fertilized, stockpiled bermudagrass forage.

Experiments were conducted to determine the effects of increasing supplement protein concentration on performance and forage intake of beef cows and forage utilization of steers consuming stockpiled bermudagrass forage. Bermudagrass pastures were fertilized with 56 kg of N/ha in late August. Grazing was initiated during early November and continued through the end of January each year. Treatments for the cow performance trials were: no supplement or daily equivalents of 0.2, 0.4, and 0.6 g of supplemental protein per kilogram of BW. Supplements were formulated to be isocaloric, fed at the equivalent of 0.91 kg/d, and prorated for 4 d/wk feeding. Varying the concentration of soybean hulls and soybean meal in the supplements created incremental increases in protein. During yr 1, supplemented cows lost less weight and condition compared to unsupplemented animals (P < 0.05). During yr 2, supplemented cows gained more weight (P = 0.06) and lost less condition (P < 0.05) compared to unsupplemented cows. Increasing supplement protein concentration had no affect on cumulative cow weight change or cumulative body condition score change. Forage intake tended to increase (P = 0.13, yr 1 and P = 0.07, yr 2) in supplemented cows. Supplement protein concentration did not alter forage intake. In a digestion trial, four crossbred steers were used in a Latin square design to determine the effects of supplement protein concentration on intake and digestibility of hay harvested from stockpiled bermudagrass pasture. Treatments were no supplement; or 0.23, 0.46, and 0.69 g of supplemental protein per kilogram of BW. Forage intake increased (P < 0.05) 16% and OM intake increased (P < 0.01) 30% in supplemented compared to unsupplemented steers. Diet OM digestibility increased (P = 0.08) 14.5% and total digestible OM intake increased (P < 0.05) 49% in supplemented compared to unsupplemented steers. Supplement protein concentration did not alter forage intake, total digestible OM intake, or apparent digestibility of OM or NDF. During the initial 30 d after first killing frost, beef cows did not respond to supplementation. However, later in the winter, supplementation improved utilization of stockpiled bermudagrass forage.

Evaluation of crosses of Holstein, Jersey or Brown Swiss sires x Holstein-Friesian/Gir dams. 2. Female liveweights

The liveweights of 100 females sired by Holstein (H), Jersey (J) or Brown Swiss (BS) bulls out of Holstein-Friesian x Gir dams of 1/2 to 3/4 Holstein-Friesian fraction were compared. The animals were kept in a single herd under the same management. The data were analyzed separately for four age categories by least squares techniques. The models for cows and heifers older than 18 months included the fixed effects of breed of sire, Bos taurus fraction, season of weighing, days in milk class (for cows only), pregnancy status class, year and the random effect of animal nested within breed of sire x B. taurus fraction subclasses. The models for younger heifers included the same effects except for lactation and pregnancy status. Based on 2937 observations, the mean weights for 0- to 6-month-old calves for the groups with H, J or BS sires were 88 +/- 1, 77 +/- 1 and 75 +/- 1 kg, respectively, the mean weights for 1-year-old heifers were 168 +/- 2, 159 +/- 2 and 155 +/- 1 kg, for 2-year-old heifers, 327 +/- 4, 303 +/- 4 and 319 +/- 4 kg, for 3-year-old heifers, 380 +/- 5, 369 +/- 8 and 390 +/- 4 kg and for cows, 464 +/- 3, 413 +/- 2 and 478 +/- 2 kg. Cubic growth curves, which were different in the three sire breed groups, satisfactorily explained the cow weight changes with age (R(2)>or=0.98). Maximum weight was attained at 7.8, 9.5 and 9.2 years in cows with H, J or BS sires. Although breed of sire effects were not significant in heifers (P>0.05), those with H sires were the heaviest up to two years of age. The females with BS or J sires had similar weights up to one year of age, but thereafter the former reached similar weights as the females with H sires and declined less after attaining the maximum weight. The cows with J sires were the lightest at all ages. Since previous results showed similar protein and fat yields per day of calving interval in the three breed of sire groups, it is suggested that the lighter J crosses may be more economic than the other groups on account of their likely lower feed maintenance costs.

Limit-feeding corn as an alternative to hay reduces manure and nutrient output by Holstein cows.

Efficiency of limit-feeding a whole shelled corn-based diet as an alternative to a conventional forage-based diet for nonlactating dairy cattle was determined. Twelve nonlactating, multiparous Holstein cows (initial BW 642+/-50 kg) were used in a randomized complete block design. Nutrient digestibility, excretion of DM, N, and P, performance of cows, and feed costs were measured. Both diets were formulated to provide equal daily intakes of NE1, protein, vitamins, and minerals, according to National Research Council recommendations. Dry matter intake was restricted by 30% for cows fed the high-corn diet compared with the high-forage diet (6.8 vs 9.6 kg/ d, respectively); therefore, concentrations of nutrients in the high-corn diet were increased to compensate for decreased DMI. Diets were fed once daily, and cows had unlimited access to fresh water. After a 28-d adaptation period, cows were placed in metabolism stalls for a 6-d total collection of feces and urine. The limit-fed, high-corn diet had a 15% greater DM digestibility than the high-forage diet. A 29% decrease in DMI for the high-corn diet vs the high-forage diet resulted in a 40% decrease in fecal DM excretion. Starch digestibility and digestibility of whole corn kernels were not affected (P > or = .62) by diet. Despite similar N intakes, total N excretion was 22% greater (P < .01) for cows fed the high-forage diet than for those limit-fed the high-grain diet. Cow weight and condition score change did not differ (P > .10) between diets. Feed costs were reduced by $.38/d with the high-corn diet vs the high-forage diet. Limit-feeding a corn-based diet is an economically and nutritionally viable alternative to forage-based diets for nonlactating Holstein cows.

Rotational vs. Continuous Stocking of Beef Cows and Calves on Mixed Endophyte-Free Tall Fescue-Bermudagrass Pasture

Endophyte-free tall fescue (Festuca arundinacea Schreb.) furnishes better animal performance than endophyte- infected grass but is less persistent under grazing, especially in mixture with common bermudagrass [Cynodon dactylon (L.) Pers]. Rotational (RS), compared with continuous (CS), stocking of endophyte-free tall fescue may improve persistence when grown with an aggressive warm season perennial grass. Four 40-acre bermudagrass pastures no-till seeded witb endophyte-free 'AU Triumph' tall fescue were used, allowing two replications to compare CS and RS methods. Rotationally stocked pastures were divided into 12 paddocks to allow 2 d of grazing and 22 d of rest. Twenty Hereford (Bos taurus)x Brangus (B. indicus x B. taurus) beef cows/40-acre pasture were maintained year around for 3 yr with additional cows added in spring and summer to maintain similar forage availability. Grazing method had no effect on cow weight change, pregnancy rate, or calf weaning weight. Pasture stocking rate and calf weaning weight per acre were 38 and 37% higher (P < 0.10), respectively, and winter hay consumption was 31% lower from rotationally stocked pastures because of better tall fescue persistence and forage availability. Crude protein (CP) and in vitro dry matter digestibility of available forage generally exceeded 8 and 50%, respectively, throughout the year. Rotational stocking appears to be useful in maintaining stands of endophyte-free tall fescue in bermudagrass pastures.

Phosphorus Supplementation of Range Cows in the Northern Great Plains

Low phosphorus (P) levels in Northern Great Plains rangeland forage combined with limited data on the P requirements of range cows (Bos taurus), precipitated 2 studies conducted to compare the performance of P supplemented and no P supplemented (control) beef cows. Phosphorus supplementation levels ranged from 4 to 8 g day-1 depending on estimated P needs at different times of the year. The 2 groups of cows previously had been involved in replacement heifer growing studies, with P treatments established 462 and 402 days, respectively, before initiation of these studies. Winter feed consisted of mixed hay, primarily smooth bromegrass (Bromus inermis Leyss.), with corn silage (Zea mays L.) fed only in 1982 and 1983 from calving to the time cows were turned on summer pasture. Summer pastures contained primarily western wheatgrass [Pascopyrum smithii (Rydb.) A. Love], needleandthread (Stipa comata Trin. and Rupr.), green needlegrass (S. viridula Trin.), blue grama [Bouteloua Gracilis (H.B.K.) Griffiths] and upland sedges (Carex spp.). The P status of cows used in these studies appeared to be estimated more reliably by forage P than by serum or fecal P. According to P levels in hay and pasture, the diets of control cows were below recommended P levels for about 9 months of the year. However, weight change differences between P supplemented and control cows during the first lactation and gestation periods were gradually lost by the end of the studies. Conception rates of control cows were slightly lower (p<0.08) in the first but not the second study. There were no differences in average calving date or calf birth weights, but P supplementation did increase (p<0.01) calf weaning weights. Cow weight changes, calf weaning weight differences, forage and serum P data, and in the first study conception rate differences indicate that Northern Great Plains forages are marginal to deficient in P for optimal production of beef cows. The most consistent benefit from P supplementation was an increase in calf weaning weights. Data also indicate that energy supplementation for 30 days after calving may increase conception rates.

Partition of nutrients and return to oestrus in lactating Bos indicus cows

This study examined the hypothesis that partitioning of nutrients towards maternal tissue growth, rather than milk production, may favour a more rapid return to cyclic ovarian activity in lactating Brahman cows. Three strategies to decrease milk production in well-fed cows were tested. Continuous infusion of the somatostatin analogue RC-121 and immunization of cows against growth hormone releasing hormone had no significant effects on milk yield, cow and calf weight change and the duration of the period of anoestrus post-calving. Restriction of udder capacity by surgical occlusion of two teats reduced milk yield by about 20% (P &lt; 0.001). During the first 6 weeks of lactation, cows with restricted udder capacity gained 0.31 kg/day compared with a loss of 0.08 kg/day by controls (P &lt; 0.05). From weeks 7-20, both groups gained at 0.4 kg/day. The duration of the period of anoestrus after calving was approximately 6 months in each group. In experiments in which calves were weaned, all cows returned to ovarian activity within 16 days of weaning. It was concluded that purebred Brahmans preferentially partition nutrients towards the mammary gland and that partially redirecting nutrients towards maternal tissue growth rather than milk secretion did not result in a more rapid return to cyclic ovarian activity.

Measurement of trypanotolerance criteria and their effect on reproductive performance of N'Dama cattle

One thousand and twenty-eight cow-year records were available from 260 N'Dama cows each having at least 2 years of monthly matching health and performance data over a 5-year period under a medium natural tsetse challenge in Gabon. Four hundred and fifty-eight calf/dam pairs were also available where the calf had been reared to weaning, both had monthly matching records and each cow had weaned at least two calves. Evaluations were carried out on effects of, and linkages between, enviromental and stress factors, number and species of trypanosome infections, curative drug treatments given, anaemia measured by packed red cell volume (PCV), and performance measured by calf weaning weight, cow calving rate and cow weight change over the lactation period. Major findings were that over the period from calf birth to weaning, while calves and their dams grazing together had similar numbers of trypanosome infections detected, the Trypanosoma vivax: T. congolense ratios were very different: 1:0.7 in calves; 1:2.8 in cows. This indicated that some ability to control the development of parasitaemia following T. vivax infection might be being acquired, from weaning onwards. In cows, relationships between lowest PCV recorded and curative drug treatments given suggested that between 20 and 32% of trypanosome-infected cows were not being identified by the buffy coat parasitological diagnostic technique. The high level of curative treatment given (to 13.7% of cows over the calendar year, and to 40% of calves from birth to weaning) will have tended to reduce the variance and linkages between aspects of infection and PCV values, especially in calves. In calves, the influence of trypanosome infections, in both calf and dam, on their respective PCV values and hence on calf weaning weight was apparent. There was a 0.91 ± 0.40 kg increase in calf weaning weight for each 1% increase in calf average PCV, and a 0.95 ± 0.39 kg increase for each 1% increase in cow average PCV. In cows, there was a similar pathway of influence of T. congolense infection through the PCV values to calving rate — not significant with T. vivax infection. There was a 3.3 ± 0.65% increase in calving rate for each 1% increase in average PCV. Repeatabilities of performance traits were in the normal range. Repeatabilities of numbers of trypanosome infections detected by the buffy coat technique were too low to have any practical significance. Repeatability of average PCV at 0.40 ± 0.03 could allow PCV when infected to be used as one criterion of trypanotolerance.

Step-Up Protein Supplementation for Beef Cows Grazing Dormant, Tallgrass Prairie

Protein supplementation contributes significantly to expenses of maintaining pregnant beef cows (Bos taurus) on winter range. Two experiments evaluated winter supplementation schemes for grazing beef cows. Dehydrated alfalfa (Medicago sativa L.) pellets (DEHY) or soybean [Glycine max (L.) Merr.] meal/sorghum [Sorghum bicolor (L.) Moench.] grain (SS) supplements were fed during the third trimester of gestation. In Exp. 1, treatments were: (i) 5.3 lb/head/d DEHY, (ii) 3.7 lb/head/d SS; (iii) 3.8 lb/head/d DEHY, and (iv) DEHY averaging 3.7 lb/head/d across the supplementation period but fed in increasing amounts with advancing gestation (step-fed) [...]

The influence of timing and the addition of urea to supplements containing DL-methionine on ruminal fermentation and cow weight change in beef cows.

A study was conducted to determine an optimal time for supplementation of DL-methionine in relation to time of forage intake by mature British breed-type crossbred cows, and two other experiments were conducted to determine whether ruminal ammonia concentration limited changes in disappearance rates in situ and ruminal functions caused by supplements containing DL-methionine. Experiments 1 and 2 used 4 x 4 Latin square designs with four cows in each experiment. Treatments in Exp. 1 were no supplement (CON), DL-methionine at feeding (0800), DL-methionine 4 h after feeding (1200), and DL-methionine 7 h after feeding (1500). Treatments in Exp. 2 were .5 kg of beet pulp (CON), .5 kg of beet pulp plus 16.5 g of DL-methionine (MET), .5 kg of beet pulp plus 16.5 g of DL-methionine and 55 g of urea (METU), and .4 kg of soybean (SOY). Experiment 3 was conducted in a 326-ha pasture with treatments of no supplement (CON), .5 kg of beet pulp plus 12.5 g of DL-methionine and 30 g of urea (METU), and .4 of kg soybean meal (SOY). In Exp. 1, in situ NDF disappearance rates of cows supplemented at 1200 and 1500 were greater (P less than .01) than those of cows supplemented at 0800. In Exp. 2, ruminal ammonia concentration was greatest (P less than .001) for METU (5.2 mg/dl) and least for CON (1.5 mg/dl). Disappearance rates in situ for DM differed (P less than .01) among treatments; METU was similar (P greater than .2) to SOY but faster (P less than .01) than MET. Disappearance rates of NDF were greatest (P less than .001) for METU-supplemented cows. In Exp. 3, DM and NDF disappearance rates were faster (P less than .10) for SOY than for METU. Cow BW change was positive for METU and SOY, and decrease in condition score was least (P less than .10) for METU- and SOY-treated cows. These studies indicate favorable ruminal responses to DL-methionine supplementation; however, the response depended on time of supplementation and ruminal ammonia concentration.

The Value of Wheat Middlings in Winter Supplements for Beef Cows

Eighty-four spring calving Hereford and Hereford x Angus cows in trial 1 and 96 in trial 2 were grazed on dormant native tallgrass pastures and were Individually fed supplements to evaluate the value of wheat middlings. In trial 1, wheat middlings (WM) were compared to soybean meal (SBM) and isonitrogenous cornlS8M mixtures (16% CP, CIS). Supplements were fed 6 dlwk from November 4 to April 21. Treatments were two levels of CP (.21 or .54kg) from SBM, WM, or CIS in a 2 by 3 factorial arrangement. Precalving and total winter cow weight changes were improved for WM and CIS compared to SBM when fed .54kg CP bUlt not the .21kg CP level. Precalving and winter cow weight and condition changes were similar for WM and CIS at both levels of CP. Pregnancy rates tended (P<.15) to be greater for WM and CIS at both levels of CPo Birth weights were greater (P<.05) for calves of cows fed supplements providing .54kg CP.Trial 2 was conducted to detlermine the amount of WM needed for cows to perform as well as when fed 1.36kg SBM. Cows were supplemented with 1.36kg SBM or 2.27,2.84, and 3.41kg of WM .daily to provide .55, .34, .44, and .55 k,g CP, respectively. Supplements were fed 6 dlwk from November 1 to April 18. Cow weight changes from November 1 to calving increased linearly (P<.01) With Increasing amounts of WM and were 20, 28, and 47kg for 2.27, 2.84, and 3.41kgld WM compared to SBM-fed cows that gained 35kg. Cow weight changes were similar from precalving to beginning of breeding. Pregnancy rates temded to be greater (P<.10) for cows fed WM than for cows fed an isonitrogenous amount of S8M. Calf birth weights increased linearly (P<.01) with increasing amounts of WM. Weaning weights of calves were similar for cows on all treatments. In conclusion, WIVI appear to be at least equal to isonitrogenous GIS blends as wint.er supplements to spring calving cows on lowqualIty forage. Linear increases in precalving. cow weight change with increasing levels of WM Indlcate that the protein andlor energy In WM IS well utilized.

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.

MILK YIELD AND COMPOSITION IN BEEF COWS AND THEIR EFFECT ON COW AND CALF PERFORMANCE IN TWO ENVIRONMENTS

Relationships of milk yield and composition of 10 specific F1 crosses of beef cows with preweaning growth of their calves and with changes in the weight and subcutaneous fatness of the cows during lactation were examined over 2 yr for a population of 120 cow-calf pairs each year at two climatically distinct locations. The crosses were represented by the Hereford × Angus (HA) and nine crosses produced by mating Charolais (C), Simmental (S), and Limousin (L) sires to cows of Hereford (H), Angus (A), and Shorthorn (N) breeding. Environmental differences were provided by two climatically distinct locations (Brandon, Manitoba; Manyberries, Alberta) with two treatments (drylot confinement, T1; pasture, T2) imposed at each location. Milk was measured at 8-wk intervals commencing 1 June and terminating 1 October (weaning). Cow weight and fat at calving were positively associated (P &lt; 0.0001) at both locations. Weight of the cow at calving was positively associated with average milk yield and calf growth rate at Manyberries (P &lt; 0.0001), but at Brandon the association was positive but not significant (P &gt; 0.05). Weight of cow at calving was positively associated with calf birth weight at Manyberries (P &lt; 0.02). Calf preweaning growth rate was directly related to birth weight (P &lt; 0.009). Calf sex had the expected effect on calf growth rate throughout lactation (M &gt; F) but milk yield of the cow was not influenced by the sex of calf reared. Percentages of the milk constituents (butterfat (BF), solids-not-fat (SNF), protein (PT), declined as milk yield increased but the reduction was significant only for PT (P &lt; 0.0005). Changes in cow weight and subcutaneous fat cover during lactation were inversely related with milk yield, the reductions in weight being significant (P &lt; 0.008) at both locations and the loss of subcutaneous fat cover significant (P &lt; 0.0001) only at Manyberries. Calf growth rate increased as milk yield increased with the largest regression coefficients at each stage of lactation provided by the estimate of average milk production for the complete lactation; however, this difference was not significant (P &gt; 0.05). The statistical model with the covariate average milk production accounted for approximately 58% of the variance for calf gain during the lactation period. The covariate alone contributed 36% of this total R2 value at Brandon and 48% at Manyberries. Simmental cross cows produced the fastest growing calves while HA and L cross cows produced the slowest growing calves at both locations. The highest milk yields were recorded for the S cross cows at both locations while HA cows were lowest at Brandon and LH the lowest at Manyberries. At both locations, the SN cows recorded the lowest values for % BF and % SNF, and the SA cows recorded the highest values for % PT. For % BF and % SNF, the HA cows were the highest at Brandon while at Manyberries, the LH cows recorded the highest values. Average milk yield (AMY) was the best milk production variable explaining variance associated with calf growth. The R2 values were higher at Manyberries than Brandon and the R2 values decreased as the lactation season progressed. The addition of any of the milk constituent variables added little to the R2 values for AMY. Key words: Milk yield, milk composition, calf growth, cow weight change, cow subcutaneous fat change

Influence of Cow Weight Change on Cow Reproductive Performance and Calf Peformance

Records covering a 12-yr period [264 cows (Bos indicus × Bos taurus); average of 21 cows/yr] were evaluated on a herd of fall-calving Brahman × Hereford F1 cows which were used primarily in forage species × stocking rate pasture evaluations. These data were analyzed to determine the effect of cow weight change during early to mid-gestation on cow and calf performance. Calf birth weights, adjusted weaning weights (205 d), calving intervals, and percent calf crop were collected annually. Additional data collected during the final year of the study consisted of cow body condition scores during early to mid-gestation, cow weight and body condition score at calving, and postpartum interval (PPI). The cows were divided into two groups based on weight loss (WL) or weight gain (WG) during early to mid-gestation. Birth weights of calves were similar (P > 0.10) for WL and WG cows. Weaning weight of the calf at side during the nutritional restriction was lower for WL than WG cows (P < 0.0001). Percent calf crop was greater for the WG than WL cows (P < 0.01). The WL cows that did conceive had longer (P < 0.0001) calving intervals than the WG cows that conceived. During the final year of data, WL cows exhibited lower (P < 0.0001) mean body condition scores during early to mid-gestation, weighed less (P < 0.002), and had lower body condition scores (P < 0.0001) at calving than the WG cows. The PPI was similar (P < 0.10) for WG and WL cows. These results indicate that weight loss during early gestation can decrease cow reproductive performance, but does not influence birth weight of the subsequent calf.

Effect of lasalocid on fall-calving beef cows.

The effects of lasalocid on fall-calving beef cows were examined in a 196-d trial that began October 12, 1983. Forty-two crossbred cow-calf pairs were stratified to six groups by breed, calving date and sex of calf. Three replications of each of two treatments, 0 and 200 mg lasalocid X head-1 X d-1, were used. The cows were fed a combination of haylage and grass hay ad libitum. The cow-calf pairs were allowed access to pasture at all times, except during the breeding season. At this time they were kept in confinement to facilitate heat detection and artificial insemination. Cow weight changes and body condition (0 = very thin, 9 = very fat) were unaffected (P greater than .10) by feeding lasalocid to the cows. Twelve-hour milk production per cow, percent fat and percent protein were each determined three times during the trial. A slight increase in milk yield was observed in treated cows (P greater than .10). Percent milk fat and protein were also unaffected by treatment (P greater than .10). Lasalocid supplementation of cows did not affect calf gain or 205-d adjusted weaning weight (P greater than .10). Average days open was evaluated for the cows. There were no differences between treatments for actual average days open (P greater than .10). No detrimental effects were observed in long-term feeding of lasalocid to fall-calving beef cows.

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.

Characterization of breeds of Bos indicus and Bos taurus cattle for maternal and individual traits.

Angus, Boran and Red Poll sires were mated to Ankole, Boran and small East African Zebu (Zebu) females to produce the cows characterized in this study, which produced calves by Friesian, Brown Swiss, Simmental, Boran and Red Poll sires. Individual traits included cow parturition weight, cow weight at weaning, cow mean weight and cow weight change from parturition to weaning; maternal traits included calf crop born percentage, preweaning viability percentage, overall viability percentage, birth weight, weaning weight, weight at 12, 18 and 24 mo and calf weight weaned per cow exposed to breeding (productivity index). Cows by Angus and Red Poll sires significantly exceeded cows by Boran sires (all cows in this comparison had Ankole and Zebu dams) in weaning weight of progeny and in cow weight at parturition and at weaning. Cows by Red Poll sires significantly exceeded cows by Boran sires in birth weight of progeny. Progeny of cows by Boran sires significantly exceeded progeny of cows by Angus and Red Poll sires in 24-mo weight. Cows by Angus and Red Poll sires did not differ (P greater than .05) in any of the traits analyzed. Cows with Ankole and Boran dams significantly exceeded cows with Zebu dams (all cows in this comparison had Angus and Red Poll sires) in progeny weight at birth, 18 mo and 24 mo and in cow weight at parturition and at weaning. Cows with Boran dams significantly exceeded cows with Zebu dams in weaning and 12-mo weight of progeny and significantly exceeded cows with Ankole dams in weaning weight of progeny. The significantly heavier weaning weight and significantly lighter 24-mo weight of the 3/4 Bos taurus progeny of cows with Angus and Red Poll sires relative to the 1/2 Bos taurus progeny of cows with Boran sires suggest that cattle that are 1/2 Bos taurus breed composition have greater general adaptation than cattle with 3/4 Bos taurus breed composition in the postweaning nutritive and climatic environment under which this experiment was conducted. Significantly heavier weights of Angus and Red Poll crossbred cows relative to Boran crossbred cows (all breeds crossed on Ankole and Zebu cows) indicate that the two Bos taurus breeds exceed the Boran (Bos indicus) breed in additive direct genetic effects for size when they have general adaptation to the environment.

Nutrient intake and efficiency of calf production by two-breed cross cows.

Individual consumption of total digestible nutrients (TDN) was measured on 105 two-breed cross cows (Hereford X Angus reciprocal crosses, HA; Simmental X Angus, SA; Simmental X Hereford, SH; Brown Swiss X Angus, BA; Brown Swiss X Hereford BH; Jersey X Angus, JA and Jersey X Hereford, JH) and their three-breed cross calves managed in drylot. Cows were 4 to 6 yr of age and mated to Charolais or Limousin bulls. Cows remained in the drylot for a period of approximately 1 yr (from weaning one year to weaning the next year). Ad libitum consumption of corn silage was allowed for about 4 h each day and fixed amounts of grain and protein supplement were fed as needed. Calf creep feed was provided during the latter portion of lactation. Compared with the average weight of HA cows (454 kg), SA cows were 7% heavier, SH, BA and BH cows were similar, while JH and JA cows were 15 and 22% lighter in weight, respectively. Total intake of TDN by cow and calf for the 365-d drylot period was greatest for the SA group (2,309 kg), exceeding that of the HA group by 11.2%. The JA group consumed 7.2% less than HA, while other groups were similar to HA in TDN intake. Daily intake of TDN for the 365-d period, expressed as a percentage of cow weight and cow weight .75, was highest for the smaller J crosses. The ratio of 365-d TDN intake to 205-d calf weight, a measure of weaning efficiency, averaged 10.0 kg/kg for JH, BH and SH, 10.5 kg/kg for HA and BA and 10.9 kg/kg for JA and SA. When TDN intake was adjusted for cow weight change, crossbred cow group was not a significant source of variation for kg TDN/205-d calf weight.

Effects of energy level and monensin on reproductive performance and lactation of beef cows

This experiment consisted of a 2 year drylot study involving 80 multiparous, suckled beef cows (40 Angus and 40 Herefords). Experimental treatments (breed, monensin and year) were arranged in 2 3 factorial to evaluate the effect of breed and monensin on reproductive performance and lactation. Cows received 85% of the NRC total digestible nutrient (TDN) requirement for the first 56 days of the 140 day trial. Cows were synchronized with Synchro-Mate B and artificially inseminated 30 days into each trial with blood samples collected for luteinizing hormone (LH) analysis from one-half of each treatment group from 24 to 36 hours after implant removal. Progesterone determinations were made on plasma samples collected at day 9 and 16 after implant removal. On day 56, milk yield estimates were obtained by the weigh-suckle-weight technique. Following these collections, energy levels were increased by allowing ad lib consumption of forage. Calves, which were removed from the cows during feeding, were given access to a 75% TDN creep ration after day 56. Milk estimates were again evaluated at 140 days. Monensin supplementation did not result in a difference in cow weight change through the restricted energy period (first 56 days) or throughout the entire 140 day period. Milk yield estimates at 56 and 140 days and calf gains throught the trial, were unaffected by monensin supplementation. Monensin resulted in no effect on conception rate or services per conception. The time of the LH peak was shifted slightly forward by monensin although not significantly. Progesterone levels were not consistently affected by monensin supplementation.