Pregnant Beef Cows Research Articles

The effects of pre- and early post-calving management on reproductive performance of beef cows

One hundred and thirty-four pregnant beef cows (liveweight = 544.3 kg ± 73 3 kg SD; condition score = 3.5 ± 0.3 SD), were randomly assigned in January to five management treatments (combinations of feed restriction and weaning time) to study the effects on calving and rebreeding performance. Twenty-seven were feed-restricted (54.7 MJ DE d−1) for the last 3 mo of pregnancy then realimented (3REST); their calves were weaned in October. Thirty were feed-restricted for the last 3 mo of pregnancy (54.7 MJ DE d−1) and the first 2 mo of lactation (99.6 MJ DE d−1), then their calves were weaned and turned out to graze in June (5REST). The remaining 77 cows (UNREST) were supplemented on range with 153.5 MJ DE d−1 from January until calving. Their calves were weaned in either August (one group of 26 calves directly into a feedlot, a second group of 26 onto unsupplemented range) or October (25 calves directly into a feedlot). All cows grazed together on the range from June onwards. After calving, the restricted (3REST and 5REST) cows were significantly lighter (464.4 and 469.5 kg vs. 506.9 kg) and thinner (condition scores 2.5 and 2.6 vs. 3.0) than the UNREST cows, but the percentage of cows calving calf mortality, assisted births calving dates, udder scores and mean birth weight of calves were not affected (P > 0.05) by pre-calving nutrition. Catch-up growth was evident in both the 3REST and 5REST cows once exposed to higher energy feeding. There were no significant effects (P > 0.05) of the management (nutrition and weaning) treatments on the following year s breeding and calving performance. It is concluded that the combinations of nutrition and weaning used in this study did not necessarily impair calving or rebreeding performance of beef cows, which calved in condition score 2.5 or above. Key words: Beef cows, feed restriction, reproduction, condition score, rebreeding, birthweight

Semi-Arid Warm-Season Grass Yield and Nutritive Value in Argentina

The use of standing dead biomass, during the winter that was produced by warm-season grasses in the previous growing season by pregnant beef cows may be an alternative to grazing systems in the semi-arid Pampean Region of Argentina. This study, conducted over 2 years, 1990 and 1991, compared the winter forage quality produced during the previous growing season for 4 warm-season grasses; switchgrass (Panicum virgatum L. cv. Pathfinder), kleingrass (Panicum coloratum L.), tetrachne (Tetrachne dregei Nees) and weeping lovegrass (Eragrostis curvula (Schrad), Nees cv. Tanganyka). Five harvests of the summer growth started after the first frost, and were spaced evenly throughout the winter period. Changes in the standing crop of dry matter were measured and subsamples of forage were divided into leaf and stem fractions. Forage quality analyses included: crude protein (CP), in vitro dry matter digestibility (IVDMD), effective rumen degradability (ED), neutral (NDF) and acid (ADF) detergent fiber and lignin. Tetrachne dregei produced forage with a higher leaf:stem ratio and of generally higher quality, than the other species, although the differences were not always significant. Its CP content was marginally below the maintenance requirements of cows. Dry matter yield of tetrachne was lower than that of weeping lovegrass, but differences were only significant in 1990. Kleingrass generally was high in quality and dry matter yield, although it was the lowest in percentage of leaves of the 4 species evaluated. Switchgrass was the least productive; the nutritive value of its forage was low, comparable or lower than that of weeping lovegrass. The first harvest date was higher in nutritive value. Although the nutritive value of leaves and stems were not compared statistically, the leaves tended to be higher than the stems. Tetrachne dregei, the best of the species evaluated in this study, is a very promising warm-season grass, which could provide nutritious forage for winter grazing systems in the semiarid Pampean Region of Argentina.

Genetic parameters for feed intake and efficiency in dry pregnant beef cows

Genetic parameters of feed efficiency and traits relative to feed efficiency for dry pregnant beef cows were estimated from data collected from 1980 to 1988 at the Elora Beef Research Centre, Guelph, Ontario. Measurements of individual feed intake were available for 90 d immediately before calving. Estimates of parameters were obtained using derivative-free restricted maximum likelihood (DFREML), with an individual-animal model with year-season, sex of fetus, parity breeding system, covariate daily backfat change, and genetic and permanent environmental effects. The data included 729 observations, 337 cows, 278 dam–maternal grand dam pairs, and 208 sires of cows. Feed efficiency for pre-calving gain of fetus was calculated as pre-calving gain relative to energy consumed for maintenance and pregnancy, with adjustment of intake for weight change by National Research Council (NRC) standards (FE) or by regression analysis (FER). Residual feed consumption was calculated as energy intake minus energy requirements, with requirements estimated by NRC standards (RFC) or by regression (RFCR). Heritabilities for Hereford alone and total data, respectively, were 0.03 and 0.16 for daily metabolizable energy intake (MEI); 0.20 and 0.44 for metabolic body weight (MBW); 0.28 and 0.22 for fetal pre-calving average daily gain (PADG); 0.11 and 0.05 for FE; 0.28 and 0.20 for FER; 0.01 and 0.04 for RFC; and 0.03 and 0.22 for RFCR. Genetic and phenotypic correlations indicated a positive association of energy intake with pre-calving fetal gain and weight of cow, although correlations with weight of cow were low. Residual feed consumption for the total data was not genetically associated with MEI or PADG, moderately associated with MBW, and highly negatively associated with FE. Key words: Genetic parameter, feed efficiency, pregnancy, beef

Response of pregnant beef cows to undegradable intake protein fed in excess of the degradable intake protein requirement (1995)

Two concurrent experiments were conducted to evaluate the effect on performance and forage intake of increasing the supply of undegradable intake protein (UIP) to pregnant beef cows already receiving sufficient degradable intake protein (DIP) to maximize forage intake. Three supplements were fed at .34% BW/day, providing .092% B W/day of DIP (level determined in previous study to maximize forage intake) and .042, .059, and .077% BW/day of UIP (low , moderate, and high UIP, respectively) . In study 1, ad libitum tallgrassprairie forage intake was measured daily from 12/1/93 to 2/10/9 4 using 18 pregnant Angus x Hereford cows. Forage intake steadily increased throughout the study, but did not vary between supplements for the first 6 weeks. However , forage intake was less during the last 4 weeks for cows offered the moderate and high UIP supplements. In study 2, 117 pregnant Angus x Hereford cows grazing dormant bluestem range were used to determine the impact of the supplements on body weight and body condition changes. Level of UIP in the supplement exerted only minimal effects on cumulative or 28-day interval changes in body weight or condition.

Effect of frequency of supplementation and protein concentration in supplements on performance and digestion characteristics of beef cattle consuming low-quality forages.

Three experiments evaluated whether effects of altered frequency of supplementation on forage use and cow performance depended on supplement CP concentration and (or) grain type when fed to cattle eating low-quality forages. All experiments included supplementation frequency (daily = 7x; three times weekly = 3x) as one factor in a factorialized arrangement of treatments. In Exp. 1 and 2, the second factor was supplement CP concentration (10, 20, 30, and 40% CP), altered by changing the ratio of soybean meal to sorghum grain in supplements. Supplements were fed at 13.9 and 14.1 kg of DM/wk for Exp. 1 and 2, respectively. In Exp. 3, the second factor was supplement grain type (sorghum grain or corn) and supplements containing 21% CP were fed at 14.8 kg of DM/wk. In Exp. 1, eight ruminally fistulated steers (456 kg) consumed wheat straw ad libitum. Pregnant beef cows grazing dormant tallgrass prairie were used in Exp. 2 (475 kg; n = 128) and 3 (504 kg; n = 120). In Exp. 1, reducing supplementation frequency decreased (P < .01) straw intake but increased (P < or = .03) DM and NDF digestion. As CP concentration in supplements increased, straw DMI (P = .06) increased quadratically, whereas DM and NDF digestion increased linearly (P < .01). In Exp. 2, increasing CP concentration in supplements enhanced cows' ability to maintain BW and condition up to calving, with decreasing magnitude of difference between treatments at higher CP concentrations (P < .01). Increasing CP in supplements fed to the dams linearly (P = .05) increased calf weaning weight in Exp. 2. In Exp. 2 and 3, reducing supplementation frequency increased (P < or = .02) winter weight loss through calving. Grain type did not significantly affect most performance variables. In summary, response to supplementation frequency was not dependent on supplement CP concentration or grain type. Daily supplementation maximized forage intake and cow performance, although the magnitude of performance differences was not large.

Ponderosa Pine Needle-Induced Abortion in Beef Cattle: Identification of Isocupressic Acid as the Principal Active Compound

A crude acid fraction isolated from the needles of ponderosa pine (Pinus ponderosa Laws) induced abortions when fed to late-term pregnant beef cows. The major components identified in this abortifacient fraction were four long-chain fatty acids (palmitic, linoleic, oleic, and stearic acids), four abietane diterpene acids (isopimaric, dehydroabietic, abietic, and neoabietic acids), and two labdane diterpene acids (imbricataloic and isocupressic acids). From this crude acid fraction isocupressic acid was isolated and dosed by gavage to five pregnant cows starting on day 250 of pregnancy. Four of the five cows aborted calves when administered isocupressic acid at dosages between 99 and 152 mglkg (twice daily). At a lower dosage of 66 mglkg no abortion occurred. No abortifacient activity was observed after a mixture of the abietane diterpene acids was gavaged at dosages of 77 and 120 mg/kg (twice daily); but at higher dosages (238 and 255 mg/kg) these compounds were toxic, and two cows died. It was concluded that the primary abortifacient constituent in ponderosa pine is isocupressic acid and that a separate toxic syndrome may occur from ingestion of high levels of some abietane diterpene acids in pine needles.

Regulation of bovine mammary growth by peptide hormones: involvement of receptors, growth factors and binding proteins

Involvement of the somatotropin (ST)/prolactin(PRL)/placental lactogen (PL) family and their mediators in regulating mammary growth in cattle was evaluated using both in vitro and in vivo models. Mitogenic activity of bovine mammary epithelial cells (BMEC) was not increased by ST, PRL or PL in vitro. Direct infusion of ST but not PRL into mammary glands of late pregnant beef cows increased mammary DNA. Exogenous treatment of steroid-primed dairy heifers with PL increased mammary DNA while PRL treatment resulted in lactogenesis but no detectable increase in mammary DNA. Insulin-like growth factor-I (IGF-I) directly increased BMEC DNA synthesis in vitro and infusion of IGF-I into mammary glands of late pregnant beef cows increased mammary growth. Epidermal growth factor and transforming growth factor-alpha increased the mitogenic response to IGF-I and are likely involved in paracrine regulation of mammary growth. IGF binding proteins are produced and secreted by BMEC and may be autocrine regulators of growth. Collectively, these data indicate that lactogenic hormone receptors are not involved in regulation of mammary growth in cattle. Increased mammary growth following ST and PL treatment was apparently mediated through local production or uptake of IGFs and/or alteration of IGF binding protein concentrations. Presently, it is not clear whether ST and PL act through local as well as distant somatotrophic receptors to alter availability and uptake of IGFs.

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) [...]

Plasma 1,25-dihydroxyvitamin D, insulin-like growth factor-1, calcium, magnesium and phosphorus concentrations in pregnant beef cows and calves from a herd with a known history of congenital joint laxity and dwarfism

An investigation was undertaken to ascertain the possibility of a relationship between calcium, inorganic phosphorus, magnesium, 1,25-dihydroxy-vitamin D [1,25(OH) 2D], and insulin-like growth factor-1 ( IGF-1) concentrations in blood plasma and occurrence of congenital joint laxity and dwarfism ( CJLD) in young cattle. Pregnant cows were fed hay (30 cows) or grass silage (122 cows) during winter months (October 15 to calving in March). Blood samples were taken from cows on seven occasions during the experiment and 48 hours after calving, and from calves at birth, and at seven, 14 and 56 days old. Five per cent of calves born (six of 122) to cows fed grass silage and none born to cows fed hay were affected by CJLD. The diet and health status of calves were not significantly (P>0·05) associated with the plasma concentration of 1,25(OH) 2D. The plasma calcium concentration declined with age of the calves (P<0·05) but was not affected by the occurrence of CJLD. Plasma phosphorus and magnesium concentrations in calves born to cows fed silage were higher (P<0·05) than in those born to cows fed hay. At birth and seven days old, plasma phosphorus concentrations were higher (P<0·05) in CJLD-affected calves than in healthy calves but the plasma concentration of IGF-1 was not different (P>0–05). It was concluded that the high plasma phosphorus concentrations in CJLD-affected calves and their dams could be related to the aetiology of the CJLD condition in calves.

Influence of summer cutting and fertilizer application on Altai wild rye in winter

The effects of summer cutting and fertilizer application treatments on Altai wild rye (Elymus angustus Trin.) yield and nutritive value in winter were examined in a 3-yr study in the Chernozemic Black soils of the foothills region in southwestern Alberta. Regrowth after harvest had significantly decreased acid detergent fiber (ADF) and increased crude protein (CP), phosphorus (P), and calcium (Ca) by January but decreased forage yield and plant height in regrowth after cutting. Fertilizer application significantly (P &lt; 0.05) increased dry matter yields and the concentration of CP, P, and Ca, while decreasing the concentration of ADF. Forage decreased in nutritive value, as determined by the concentration of each constituent, until November; after that, changes were no longer significant (P &lt; 0.05). However, the effects of either fertilizer or cutting treatments on the nutritive value were generally maintained to the end of the sampling period in March. Fertilizer application made access to standing forage easier for cattle in winter, as defined by plant height, but summer cutting reduced it. Cutting and fertilizer application can be used to improve the nutritive value of forage in winter to meet the requirements of dry pregnant beef cows, but this requires substantial fertilizer application. Rather than applying high rates of fertilizer, it may be advantageous to supplement nutrients to livestock on winter pasture.Key words: Winter grazing, forage quality, weathering losses

Ponderosa pine needle-induced parturition in cattle: analysis for presence of mycotoxins

Ponderosa pine (Pinus ponderosa) needles were fed to pregnant beef cows. Mean gestation lengths of 250.6 days for winter pine needles (PN) and 253.2 days for summer PN were reduced (p < 0.001) compared to controls (274.8 days). The levels of nine mycotoxins in fresh Ponderosa PN from trees, old PN from the ground, dry PN from trees, and PN collected from trees cut in the winter and summer were below detectable limits. The mycotoxins evaluated included aflatoxins BI, Bz, and GI, zearalenone, zearalenol, ochratoxin, T-2 toxin, diacetoxyscirpenol (DAS), and deoxynivalenol (DON). All of the collections of PN analyzed were either known to induce or believed to induce abortion in cattle. Inadequate cleanup prevented evaluation of zearalenone and zearalenol in winter-collected PN and dry PN from trees and T-2 toxin and DAS in winter-collected PN, fresh PN collected from trees, old PN from the ground, and dry PN collected from live trees. Pine needles collected from trees cut in the summer induced early parturition in 100% of the pregnant cows fed these PN and were successfully evaluated for all nine mycotoxins; however, levels were below detectable limits. The mycotoxins evaluated in this study do not appear to be involved in PN abortion.

THE PERFORMANCE OF PREGNANT BEEF COWS RELYING ON SNOW AS A WATER SOURCE

Body mass change, water influx, metabolic heat production and rectal temperature were measured in four pregnant beef cows offered only snow as a water source (snow cows) and in four pregnant beef cows that also had access to heated water (water cows). The study was carried out during winter (December to March) in Alberta, Canada. There was no difference between treatment groups in any of these measurements indicating that the snow cows were obtaining adequate water to satisfy their requirements and that no added nutrient energy was required to melt the snow and bring the water to body temperature. Milk yield in the two groups, measured in early spring when water was available to all cows, was similar as was the growth rate of the calves. Milk yield averaged 8.2 kg d−1 during weeks 2–4 of lactation and 4.6 kg d−1 during weeks 14–16. Average daily gain from birth to weaning (6 mo) of calves suckling the snow cows was 0.74 kg and of calves suckling the water cows was 0.70 kg. It was concluded that there was no detrimental effect of withholding liquid water from pregnant beef cows when snow is available and that cows can use snow as their only water source for lengthy periods of time during winter. Key words: Pregnant cows, snow, water, water influx, metabolic heat production

Orientation to the sun of British and exotic breed cross cows during the winter

Orientation to the sun's rays and north-south-located feed trough of > 170 pregnant beef cows of 15 breed crosses was examined on 81 occasions during two Canadian winters. Orientation to the sun's rays was more pronounced than orientation to the feed trough and the percentage of cows standing within 30° of perpendicular to the sun's rays was greatest (64%) on cold sunny days. Orientation of cows to the sun's rays or feed trough was not influenced by breed cross.

Grazing behavior responses of rangeland beef cows to winter ambient temperatures and age

A trial was conducted on Montana native rangeland to examine the effects of cow age and ambient air temperatures on mid-winter grazing activity of pregnant beef cows. Cows were fitted with vibracorders and pedometers for 50 continuous days in January and February to monitor daily grazing time ( DGT) and distance traveled. Three-year-old cows grazed 0.7 h day −1 longer ( P<0.005) and traveled 0.85 km day −1 further ( P<0.05) than 5-and 7-year-old cows. Total DGT averaged 8.8 h day −1 across ages and was insensitive ( P>0.05) to mean ambient temperature departures (either increases or decreases) from average temperatures of the previous 1–20 days. DGT did not remain below 8 h day −1 for more than one successive day. However, examination of grazing times within daily periods indicated significant linear respones to temperature changes. Morning (07.01–13.00 h) grazing times exhibited variable responses ( P<0.05) to temperature departures from averages across the previous 17, 19 and 20 days. Grazing times during afternoons (13.01–19.00 h) and evenings (19.01–07.00 h) declined ( P<0.05) when temperatures either increased or decreased from averages of the previous 6–10, and 1, 2 and 4 days, respectively. Only 17% of DGT occurred during the evening period. We concluded that in the foothill grasslands of the Northern Rockies, range beef cows maintained consistent total grazing time despite fluctuating mid-winter temperatures (8 to −26°C) and that cow age influenced grazing activity.

Performance of Fall-Calving Cows and Their Calves Grazing Fescue-Based Forage Systems

Tall fescue (Festuca arundinacea Schreb.), a perennial cool season grass, is well adapted to a wide range of soil and climatic conditions. Stockpiled (accumulated growth) tall fescue has been grazed successfully by dry pregnant beef cows in winter, but stockpiled fescue use by lactating cows has not been reported. Twenty-four, 3-acre pastures stocked with 3 or 4 fall-calving cows and their calves were used in five grazing trials from 1980 to 1984. Four forage system treatments were evaluated: (System 1) ‘Kentucky 31’ tall fescue + red clover (Trifolium pratense L.) + ladino clover (Trifolium repens L.) with fall N fertilization and stockpiling; (System 2) Fescue + ladino and red clovers + ‘Kobe’ lespedeza [Lespedeza striata (Thunb.) H. & A.]; (System 3) Fescue + red and ladino clovers + a small creep pasture for the calves consisting of rye (Secale cereale L.) + annual ryegrass (Lolium italicum L.) + crimson clover (Trifolium incarnatum L.); (System 4) ‘Tifton 44’ bermudagrass Cynodon dactylon (L.) Pers.] + fescue + red and ladino clovers + N fertilization. Cows (Bos taurus) were purebred Angus with calves sired by Angus, Hereford, or Simmental bulls. Animals were allotted to systems at the end of the calving season (December) and removed in early July. When forage growth was inadequate to meet animal nutrient requirements, hay produced on the experimental pastures was fed. Calf 240-d adjusted weights and average daily gain (ADG) were similar among systems. There was no effect of genotype on calf performance. The ADG's of cows grazing Systems 1, 2, and 3 during 1980 to 1983 were 0.23, 0.18, and −0.05 lb/d, and those of cows grazing Systems 2, 3, and 4 during 1982 to 1984 were −0.05, −0.19, and 0.11 Ib/d, respectively. In System 3, calf creep pastures (17 to 25% of total) probably were larger than needed, and cow pastures were not large enough. Cow-calf pairs grazing System 1 pastures required less hay than those grazing Systems 2 and 3 in 1980 to 1983. Cow-calf pairs grazing System 4 pastures required more hay than those grazing Systems 2 and 3 in 1982 to 1984. Results from this study support using forage systems of fescue + clover + N for fall stockpiling, and of fescue + legumes, for maintaining performance of fall calving cows and their calves.

Prediction of calving date in beef cows by real-time ultrasonic scanning.

Three hundred pregnant beef cows between 35 and 125 days of gestation were scanned ultrasonically and their calving dates were predicted from measurements of fetal parts. The mean difference between the actual and predicted calving dates was 0.9 day with a standard deviation of 9.0 days. The accuracy and precision of the prediction of calving date were sufficient to be of benefit in the management of cows in late pregnancy and at calving.

Fresh and dried brewers' grains as protein supplements to barley straw diets given to pregnant beef cows

Two experiments were conducted to compare the rumen degradability of the dry matter (DM) and nitrogen (N) in fresh (FBG) and dried brewers' grains (DBG) and their effects with or without urea on the voluntary intake of straw by pregnant beef cows. In Experiment 1, degradability values of DM and N, calculated from both exponential and linear equations, were similar for the two forms of brewers' grains. In Experiment 2, when pregnant beef cows were given 2.2 kg DM of either FBG or DBG, either unsupplemented or supplemented with 0.1 kg urea to increase the rumen degradable protein from ∼ 300 to ∼ 600 g, the two forms of grains promoted similar intakes of straw. Urea addition did not improve the voluntary intake of straw, but it increased blood ammonia concentrations. Significant increases in rumen ammonia nitrogen ( P < 0.05) and plasma urea ( P < 0.01) were associated with increases in RDP intake. Plasma urea concentrations also increased significantly ( P < 0.001) with increasing rumen ammonia nitrogen concentrations.

Serum and ruminal fluid characteristics of beef cows grazing oat pastures and supplemented with or without lasalocid.

Thirty-two mature, pregnant beef cows (avg age 8 yr, body wt 550 kg) grazing oat pastures were used to determine the effects of lasalocid on serum mineral and ruminal fluid volatile fatty acid (VFA) concentrations. Cows were blocked by breed type and assigned randomly to eight, 2-ha pastures containing oat forage from December 17, 1985 to May 6, 1986. The cows were fed .25 kg of ground corn with or without 200 mg of lasalocid daily. Based upon analyses of forage mineral composition (.53, .25, .14, .3 and 2.5% of dry matter for Ca, P, Mg, Na and K, respectively), all macrominerals except Mg were in sufficient quantities to meet the requirement for lactating cows. Lasalocid supplementation did not affect serum Mg, K or Zn concentrations (P greater than .05). During the April sampling, serum Ca was higher (P less than .05) and serum Na was lower (P less than .05) in cows supplemented with lasalocid compared with controls. The molar proportion of acetate was decreased (P less than .05) in ruminal fluid of cows fed lasalocid by d 56 (February 11); the molar proportions of acetate and butyrate were decreased (P less than .05), which decreased (P less than .05) the acetate: propionate ratio by d 84 (March 11) of supplementation. This study suggests that lasalocid is effective in altering ruminal VFA and serum mineral concentrations in cows grazing small grain forages.

Relative Winter Forage Quality of Selected Bermudagrass Cultivars1

Bermudagrass [Cynodon dactylon (L.) Pers.] forage is often stockpiled or accumulated in situ for use during winter. Very little information is available on the quality of such forage as affected by cultivar or age. This study reports results of two experiments conducted to: (i) determine relative quality of stockpiled forage of selected bermudagrass cultivars as indicated by in vitro dry matter disappearance (IVDMD) and crude protein (CP) concentrations, and (ii) monitor dormant season patterns of change in IVDMD and CP. Three cultivars (Alicia, Hardie, and Midland), two locations, and four sampling dates in the winter of 1975–1976 were included in Experiment 1. In Experiment 2, three cultivars (Hardie, Midland, and Tifton 44) were evaluated at six locations on four sampling dates in the winter of 1981–1982. Sampling in each experiment began in mid November and continued at 30‐day intervals through mid‐February. Hardie usually had higher IVDMD than the other cultivars throughout the sampling period in both experiments. There was no difference among cultivars in CP concentration in either experiment. The trend in change of both the IVDMD and CP concentrations through the winter was a decrease, but the changes were not linear, generally being best described by cubic equations. No consistent differences among cultivars in rate of change in either IVDMD or CP were found. None of the cultivars maintained high enough IVDMD levels through winter to supply minimum energy requirements for dry pregnant mature cows. Except at Mangum in Experiment 1, all cultivars maintained high enough CP levels to meet the minimum requirements of dry pregnant beef cows.

A note on the effects of dietary protein degradability in the rumen on the voluntary intake and digestibility of barley straw by lactating beef cows

In a previous experiment with pregnant beef cows (Alawa, Fishwick, Parkins, Hemingway and Aitchison, 1986) when equal amounts of crude protein (CP) were supplied from a range of concentrates providing different amounts of rumen-degraded protein (RDP), the voluntary intake of barley straw dry matter (DM) and the metabolizable energy (ME) obtained from straw were positively and significantly correlated with the intake of RDP. Whilst increasing proportions of rumen-undegraded protein (UDP) have been shown to increase the milk yield of ewes (Robinson, McHattie, Calderon Cortes and Thompson, 1979) the response of lactating beef suckler cows to UDP in terms of milk yield is not clear. There is an increasing interest in the use of peas as a protein supplement but they have not been compared with more conventional protein sources. Accordingly these present experiments were conducted to study the response of lactating beef cows and their calves to proteins from different sources providing different amounts of RDP and UDP.