Relationship between terrain use and performance of beef cows grazing foothill rangeland

A study was conducted on foothills rangeland to determine whether grazing patterns differed among cow breeds and to determine whether there was a relationship between individual grazing patterns and performance of beef cows. Hereford (HH), Tarentaise (TT), 3/4 Hereford x 1/4 Tarentaise (3H1T), 1/2 Hereford x 1/2 Tarentaise (HT), and 1/4 Hereford x 3/4 Tarentaise (1H3T) cows were observed during the summers of 1997 (n = 183) and 1998 (n = 159). Locations of individual cows were recorded two to three times per week during 1.5- to 2.5-h periods in the morning by observers on horseback. Statistical models included cow breed, age, and nursing status. Data from each year were analyzed separately. During 1997 and 1998, nonlactating cows were located at greater (P < 0.05) vertical distances from water than lactating cows. In 1998, nonlactating cows used steeper (P < 0.05) slopes than lactating cows. However, nonlactating cows did not travel as far horizontally from water (P < 0.05) as lactating cows in 1997. Younger cows (3 yr) traveled further (P < 0.05) from water both vertically and horizontally than older cows (5+ yr) in 1997, but not during 1998. Tarentaise and 1H3T cows were observed at greater (P < 0.05) vertical distances from water than HH cows during both years of the study. During 1998, TT and 1H3T cows used steeper (P < 0.05) slopes than HH cows. Using residual correlations, there were no consistent relationships between topographic aspects of individual grazing locations and cow weight, height, and body condition score. In 1997, cows with earlier calving dates and correspondingly heavier calf weaning weights used areas that had greater vertical distances to water; however, in 1998 there were no relationships (P > 0.05) of calving date and weaning weight with cow location. During both years, pregnant and nonpregnant cows used terrain similarly (P > 0.05), which suggests that cow reproductive performance was not related to terrain use. Grazing patterns in foothills rangeland varied among cow breeds. Performance of cows that used more rugged topography was similar to cows using gentler terrain.     

Botanical Composition of Yearling-Steer and Mature-Ewe Diets in the Kansas Flint Hills

Awareness of herbivore diet composition is an essential element of rangeland stewardship. Objectives of our experiment were to characterize diet selection by yearling steers and mature ewes grazing native tallgrass prairie, changes in dietary preferences that occurred with advancing season, and overlap in selection patterns between ewes and steers. Eight contiguous native tallgrass pastures (31 ± 3.3 ha) were grazed by yearling beef steers (n = 279 per yr) from 15 April to 15 July for two grazing seasons. Mature ewes (n = 813 per yr) subsequently grazed four of the eight pastures (0.15 ha per ewe) from 1 August to 1 October each year. Beginning 1 May, five fresh fecal pats were collected along four permanent transects per pasture at 2-wk intervals until steers were removed on 15 July. Subsequently, fecal grab samples were collected from 25 designated ewes per pasture on 15 August and 15 September. Microhistological analyses were conducted on fecal samples to estimate dietary botanical composition, using 17 grass, forb, and browse species from the experimental site as reference standards. Botanical composition of pastures was estimated annually in October. Diet selection was evaluated using Kulcyznski’s Similarity Index. The proportions of total graminoids and total forbs in steer diets were not different (P = 0.37) among sampling periods. Steer diets were dominated by graminoids (≥ 88.4% of diets) throughout the experiment. Steers and ewes exhibited strong preference for Bouteloua gracilis, Buchloe dactyloides, Dalea purpurea, and Liatris punctata. Ewes also demonstrated strong preferences for Vernonia baldwinii and Ambrosia artemisiifolia. Steers avoided Lespedeza cuneata and Symphyotrichum ericoides, whereas ewes did not avoid any of the reference standards. Ewes selected approximately equal proportions of graminoids and forbs (58% and 42% of diets, respectively), and proportions did not differ (P = 0.67) between sampling periods. Diet selection by mature ewes and yearling steers overlapped by 65% under the conditions of our experiment.     

Bison and Cattle Grazing Impacts on Grassland Stream Morphology in the Flint Hills of Kansas

Despite a shift from yr-round bison grazing throughout the Great Plains before European settlement to extensive seasonal cattle grazing, little is known about ungulate grazing impacts on grassland streams. In this study we 1) determine whether grazing management is a significant driver of grassland stream morphology within the Flint Hills Ecoregion (Kansas, United States); 2) determine if yr-round bison grazing (the precolonial condition) and seasonal cattle grazing (the currently dominant grazing practice in the region) result in distinct stream morphology; and 3) determine if the introduction of cattle into ungrazed watersheds produces significant changes to channel morphology. We use a replicated watershed-scale study design and survey 17 streams across four grazing treatments (ungrazed, long-term bison grazed [yr-round], long-term cattle grazed [seasonal], and newly cattle grazed [seasonal]). Baseline geomorphic surveys were completed in 2010 following consistent grazing management since 1992, and resurveys were completed in 2011 and 2013 to determine short-term grazing impacts. Under the conditions of the experiment, we did not detect significant differences (P > 0.10) in channel morphology or stream bed substrate size among grazing treatments following nearly 2 decades of consistent grazing management. Cattle introduction into ungrazed watersheds resulted in modest (P < 0.05) stream widening (0.19 m, 3.9%) following two grazing seasons. Bison grazed watersheds also experienced modest (P < 0.05) stream widening (0.20 m, 5.1%) during the resurvey period. Stream widening from 2010 to 2013 within newly cattle-grazed and long-term bison-grazed treatments indicates that cattle and bison are capable of producing moderate alterations to grassland stream morphology over short time periods. However, longer time periods containing more diverse hydrologic conditions may be necessary to generate larger geomorphic changes between surveys. Although we detected modest changes to stream morphology in response to grazing over short time periods, overall, stream morphology does not vary among grazing treatments in the study area.     

Effects of animal and supplement characteristics on average daily gain of grazing beef cattle

Effects of animal gender and age, use of a growth stimulant, and supplementation with grain alone or grain plus other substances on ADG by growing beef cattle grazing bermudagrass paddocks with sod-seeded rye, wheat, and ryegrass were determined. Two grazing experiments (Exp. 1: late winter through mid-spring; Exp. 2: late spring through mid-summer) were conducted. Experiment 1 used 96, 12- to 13-mo-old Simmental-cross calves (heifers, 240 kg; steers, 272 kg), half of which were implanted with zeranol. Within each implant treatment, cattle received no supplement or .5% BW (DM) of ground corn alone or plus a mix of protein meals, zinc sulfate, thiamin-HCl, or salt. Daily gain was higher (P less than .05) with than without supplementation and was similar (P greater than .10) among supplement treatments. In Exp. 2, 96 crossbred beef steers, approximately 7 (230 kg) or 15 mo old (250 kg), were not supplemented (control) or received .5% BW (DM) of ground corn on d 1 to 84 (C-C), corn plus a protein meal mix on d 1 to 84 (CP-CP), corn on d 43 to 84 (O-C), corn plus the protein meal mix on d 43 to 84 (O-CP), or corn on d 1 to 42 and corn plus the protein meal mix on d 43 to 84 (C-CP). Daily gain on d 1 to 84 was affected (P less than .05) by supplement, age, implant, and the supplement x implant interaction (nonimplanted: .37, .56, .68, .40, .49, and .49; implanted: .37, .62, .54, .49, .70, and .71 kg for control, C-C, CP-CP, O-C, O-CP, and C-CP, respectively).     

Influence of protein supplementation frequency on cows consuming low-quality forage: performance, grazing behavior, and variation in supplement intake

The objectives of this research were to determine the influence of protein supplementation frequency on cow performance, grazing time, distance traveled, maximum distance from water, cow distribution, DMI, DM digestibility, harvest efficiency, percentage of supplementation events frequented, and CV for supplement intake for cows grazing low-quality forage. One hundred twenty pregnant (60 +/- 45 d) Angus x Hereford cows (467 +/- 4 kg BW) were used in a 3 x 3 Latin square design for one 84-d period in each of three consecutive years. Cows were stratified by age, BCS, and BW and assigned randomly to one of three 810-ha pastures. Treatments included an unsupplemented control (CON) and supplementation every day (D; 0.91 kg, DM basis) or once every 6 d (6D; 5.46 kg, DM basis) with cottonseed meal (CSM; 43% CP, DM basis). Four cows from each treatment (each year) were fitted with global positioning system collars to estimate grazing time, distance traveled, maximum distance from water, cow distribution, and percentage of supplementation events frequented. Collared cows were dosed with intraruminal n-alkane controlled-release devices on d 28 for estimation of DMI, DM digestibility, and harvest efficiency. Additionally, Cr2O3 was incorporated into CSM on d 36 at 3% of DM for use as a digesta flow marker to estimate the CV for supplement intake. Cow BW and BCS change were greater (P < or = 0.03) for supplemented treatments compared with CON. No BW or BCS differences (P > or = 0.14) were noted between D and 6D. Grazing time was greater (P = 0.04) for CON compared with supplemented treatments, with no difference (P = 0.26) due to supplementation frequency. Distance traveled, maximum distance from water, cow distribution, DMI, DM digestibility, and harvest efficiency were not affected (P > or = 0.16) by protein supplementation or supplementation frequency. The percentage of supplementation events frequented and the CV for supplement intake were not affected (P > or = 0.58) by supplementation frequency. Results suggest that providing protein daily or once every 6 d to cows grazing low-quality forage increases BW and BCS gain, while decreasing grazing time. Additionally, protein supplementation and supplementation frequency may have little to no effect on cow distribution, DMI, and harvest efficiency in the northern Great Basin.     

Influence of sward height, daily timing of concentrate supplementation, and restricted time for grazing on forage utilization by lactating beef cows

To establish the effect of sward height, concentrate feeding time, and restricted time for grazing on forage utilization by grazing cattle, 32 crossbred beef (24 Angus and eight Hereford) cows (632 kg BW) and calves (104 kg BW) were grouped by weight and calving date. They were assigned randomly to two sward height treatments (4 to 8 or 8 to 12 cm), replicated four times. The herbage comprised mainly Kentucky bluegrass, orchardgrass, some forbs, and white clover. The cows were restricted to 12 h/d grazing (0700 to 1900) or unrestricted to 24 h/d grazing and fed a concentrate supplement (4.1 kg DM.cow(-1).d(-1), approximately 0.65% of BW or 33% of total DMI) either at 0700 or 1800. The experiment was repeated over three 15-d periods in May, June/July, and August 2000. The herbage on high sward height pasture was higher (P = 0.06) in NDF and ADF and lower (P < 0.01) in CP than low sward height herbage. For cows restricted to 12 h/d grazing, supplementing at 0700 as opposed 1800 resulted in greater (P = 0.04) forage DMI (8.6 vs. 8.1 kg/d), whereas cows that were unrestricted showed little change (8.2 kg/d at 0700 vs. 8.4 kg/d at 1800). Supplementing at 1800 as opposed to 0700 resulted in greater (P = 0.03) herbage DM digestibility (67.7 vs. 64.5%) for cows on high sward height, whereas cows on low sward height exhibited minimal differences (65.4% at 1800 vs. 66.3% at 0700). Cows restricted to 12 h/d grazing and supplemented at 0700 as opposed to 1800 resulted in greater (P = 0.06) digestible DMI (5.0 vs. 4.7 kg/d), whereas unrestricted cows exhibited the opposite response (4.6 kg/d digestible DMI at 0700 vs. 4.9 kg/d at 1800). Supplementing at 1800 as opposed to 0700 increased the time spent grazing to a greater (P = 0.09) extent for restricted than for unrestricted cows. When forage availability or grazing time was limiting (due to a low forage allowance and restricted access to forage, respectively) supplementing concentrates at 0700 resulted in greater forage utilization and intake rate because of increased forage DMI, DM digestibility, and digestible DMI. However, when forage or grazing time was not limiting, supplementing concentrates at 1800 resulted in greater forage utilization because of increased forage DM digestibility.     

Time budget, social and ingestive behaviours expressed by native beef cows in Mediterranean conditions

In order to evaluate the degree of adaptability of three native cattle breeds to the natural pastures of southern Italy, the diurnal grazing behavioural pattern was monitored on 84 multiparous cows: 28 Podolian (14 suckling and 14 non-suckling), 28 Chianina (14 suckling and 14 non-suckling) and 28 Romagnola (14 suckling and 14 non-suckling). From August to October 2009 ten sessions of 9 h of behavioural observations were performed, from 07.00 to 19.00 h, through continuous focal animal recording method. Every hour, bite rate was recorded and bite mass and botanical preferences were determined on hand-plucked samples. Chianina cows selected proportionally more percent legumes than Romagnola and Podolian animals (P < 0.01), whereas Podolian cows chose a higher percentage of ferns (P < 0.05). Grasses represented a large proportion of the diet ingested by cows; these plant species were predominantly ingested in a late stage of maturation, which, in turn, induced the animals to take larger bites. Conversely, bite rate was positively related to high quality forages and negatively related to bite mass. Due to low genetic diversity and “allelo-mimetic” behaviour, no marked differences were observed among Chianina, Romagnola and Podolian breeds in terms of activity budget, ingestive behaviour and chemical composition of the diet as assessed through hand plucking. Based on rough estimations, all three breeds were able to reach the minimum ingestion levels needed to cover their maintenance and productive requirements of energy and protein. The three genotypes spent most of their time on grazing activity, followed by walking, whereas less time was spent resting. Animals were more active during mornings and afternoons in terms of grazing and walking (P < 0.05). Vocalizations were not influenced by breed but were significantly more frequent in cows with calf (4–5 months of age) than in non-suckling animals (P < 0.001). The presence of calf had no significant effect on the other behavioural variables. Cows from different breeds expressed preferential spatial relationships with other members of the herd. These results along with the low levels of agonistic and non-agonistic interactions occurring between herd-mates suggest that extensive systems based on grazing allow social stability, expression of species-specific behaviours and fulfilment of maintenance and productive requirements of cows from native breeds.     

Effects of protein-energetic supplementation frequency on growth performance and nutritional characteristics of grazing beef cattle

Two experiments were conducted to evaluate reduced supplementation frequencies for grazing beef cattle in rainy season. In experiment 1, evaluating the nutritional parameters, four rumen-cannulated Nellore bulls (BW = 410 kg) were used. In experiment 2, evaluating animal performance, 48 Nellore bulls (BW = 358 kg) were used. The treatments were as follows: mineral supplement (MS) alone and MS plus protein-energy supplement provided 3×, 5× and 7×/week. Supplementation frequency did not affect (P > 0.05) intake and digestibility. Average daily gain was greater (P < 0.001) to supplementation compared with MS. The supplementation 5×/week resulted in greater weight gain per hectare (9.24) and higher economic returns during the study period (1.64%) compared to other supplementations. Supplementation 5×/week increased animal performance and positively influenced economic returns.     

Effects of pre-feeding of a corn silage-based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows

Four Holstein cows were used to determine the effect of timing of the feeding of a corn silage (CS)‐based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows. The cows were fed the supplement 2 h before grazing (pre‐grazing) or immediately after grazing (post‐grazing). Cows were grazed for 5 h per day under a rotational grazing system. There was no difference in the herbage and total feed intake between treatments. The milk protein yield for pre‐grazing tended to be higher than that for post‐grazing, whereas the milk yield did not differ between treatments. The total nitrogen intake for pre‐grazing tended to be higher than that for post‐grazing (P = 0.06). There was no difference in the urinary nitrogen output between treatments, whereas the proportion of urinary nitrogen output : total nitrogen intake for pre‐grazing tended to be lower than that for post‐grazing (P = 0.06). The milk nitrogen output and nitrogen retention for pre‐grazing tended to be higher than that for post‐grazing (milk nitrogen, P = 0.06; nitrogen retention, P = 0.05). Nitrogen utilization of grazing dairy cows was improved by feeding a CS‐based supplement before grazing.     

Influence of supplementation method on forage use and grazing behavior by beef cattle grazing bluestem range.

Two 25-d trials (late summer and early winter) were conducted to determine the influence of supplementation method on forage use and grazing behavior. Fifteen ruminally and 12 esophageally fistulated steers (316 and 400 kg, respectively) were blocked by weight and assigned randomly to one of three treatments: 1) self-feeding supplement (via Calan gates) with salt as a limiting agent; 2) daily hand-feeding supplement plus salt; and 3) daily hand-feeding supplement without salt. Supplement intake was restricted to .95 kg.steer-1.d-1 with .23 and .40 kg of salt.steer-1.d-1 during summer and winter, respectively. Neither season nor supplementation method affected forage (1.64% of BW) or total (1.89% of BW) OM intake (P greater than .10). Total OM digestibility was greater (P less than .05) in the summer, in salt-supplemented steers, and when steers were self-fed supplement. Digestibility of NDF was greater (P less than .05) in the summer than in early winter, but did not differ among treatments (P greater than .10). Fluid dilution rate was greater (P less than .05) for salt-fed and self-fed steers during the summer but similar among treatments (P greater than .10) during the winter. Total VFA concentrations did not differ among treatments during summer, but were slightly greater (P = .07) in hand-fed steers during the winter. Steers fed supplements containing salt consistently displayed lower (P less than .01) acetate:propionate ratios, and self-fed steers had lower (P less than .01) acetate:propionate ratios during the summer. Ruminal ammonia concentrations did not differ (P greater than .10) among treatments and between periods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance of beef cows receiving cull beans, sunflower meal, and canola meal as protein supplements while grazing native winter range in Eastern Colorado

A 2-yr grazing performance study was conducted in Eastern Colorado to evaluate the effects of feeding raw cull beans (Phaseolus vulgaris) or canola meal, compared to sunflower meal, to beef cows grazing dormant, native winter range on body weight and body condition score (BCS) change, reproductive performance, and calf performance. Ninety-five pregnant, spring-calving crossbred cows (541 +/- 51 kg) in 1995 to 1996 and 65 cows (602 +/- 60 kg) in 1996 to 1997 were randomly assigned to one of five treatments (19 and 13 cows per treatment in 1995 to 1996 and 1996 to 1997, respectively): 1) unprocessed Great Northern beans to supply 182 g/d of CP (GNB); 2) canola meal to supply 182 g/d of CP (CM); 3) a mixture of Great Northern beans and sunflower meal, each to supply 91 g/d of CP, for a total of 182 g/d of CP (MIX); 4) sunflower meal to supply 182 g/d of CP (SFM+); and 5) sunflower meal to supply 91 g/d of CP (SFM-). Cow weight and body condition performance were broken into a gestation and a lactation phase in 1995 to 1996; calves were weighed at birth, at the end of the lactation phase in April, and at weaning the following September. Only gestation performance was monitored in 1996 to 1997, and subsequent calf birth and weaning weight were recorded. The SFM- group lost more weight during the gestation phase than other treatments (P < .05), yet no differences were detected for gestation phase daily BCS change, calf birth weight, lactation phase daily weight change, lactation phase daily BCS change, first-service conception rate to AI, or overall pregnancy rate. Off-test calf weight was higher in April for calves from dams of the SFM+ and CM treatments than for calves from dams on the GNB or SFM- treatments (P < .05), and calves from cows on the CM treatment were heavier in April than calves from cows on the MIX treatment (P < .05). No differences in calf weight were present at weaning. Consumption of beans by cows on the GNB treatment was low because of palatability problems. Mixing the beans with sunflower meal in the MIX treatment eliminated this problem. Canola meal, Great Northern beans, or a combination of sunflower meal and Great Northern beans were comparable to sunflower meal as protein supplements for beef cows grazing native winter range, despite obvious palatability problems with the beans.     

Effect of supplementation frequency and supplemental urea level on dormant tallgrass-prairie hay intake and digestion by beef steers and prepartum performance of beef cows grazing dormant tallgrass-prairie

Effect of supplementation frequency and supplemental urea level on forage use (Exp. 1) and performance (Exp. 2 and 3) of beef cattle consuming low-quality tallgrass-prairie were evaluated. For Exp. 1 and 2, a 2 x 2 factorial treatment structure was used, such that two supplements (30% CP) containing 0 or 30% of supplemental degradable intake protein (DIP) from urea were fed daily or on alternate days. In Exp. 1 and 2, supplement was fed at 0.41% BW daily or at 0.83% BW (DM basis) on alternate days. For Exp. 3, a 2 x 4 factorial treatment structure was used, such that four supplements (40% CP) containing 0, 15, 30, or 45% of supplemental DIP from urea were fed daily or 3 d/wk. Supplements were group-fed at 0.32% BW daily or at 0.73% BW (DM basis) 3 d/wk. In Exp. 1, 16 Angus x Hereford steers (initial BW = 252 kg) were blocked by BW and assigned to treatment. Urea level x supplementation frequency interactions were not evident for forage intake, digestion, or rate of passage. Forage OM intake (OMI) and total digestible OMI (TDOMI) were not significantly affected by treatment. Total-tract digestion of OM (P = 0.03) and NDF (P = 0.06) were greater for steers supplemented daily. In Exp. 2, 48 Angus x Hereford cows (initial BW = 490 kg) grazing winter tallgrass prairie were used. Significant frequency x urea interactions were not evident for BW and body condition (BC) change; similarly, the main effects were not substantive for these variables. In Exp. 3, 160 Angus x Hereford cows (initial BW = 525 kg) grazing dormant, tallgrass prairie were used. Supplement refusal occurred for cows fed the highest urea levels, particularly for cows fed the supplement with 45% of the DIP from urea 3 d/wk, and supplement refusal increased closer to calving. A frequency x urea interaction (P = 0.02) was observed for prepartum BW changes. As supplemental urea level increased, prepartum BW loss increased quadratically (P = 0.02); however, a greater magnitude of loss occurred when feeding supplements containing > or = 30% of DIP from urea 3 d/ wk. Cumulative BC change followed a similar trend. In conclusion, moderate protein (< or = 30% CP) supplements with < or = 30% of supplemental DIP from urea can be fed on alternate days without a substantive performance penalty. However, infrequent feeding of higher protein (> 30% CP) supplements with significant urea levels (> 15% of DIP from urea) may result in decreased performance compared with lower urea levels.     

Influence of dose, frequency, and duration of infused gonadotropin-releasing hormone on secretion of luteinizing hormone and follicle-stimulating hormone in nutritionally anestrous beef cows.

Nutritionally induced anovulatory cows were ovariectomized and used to determine the relationships between dose, frequency, and duration of exogenous gonadotropin-releasing hormone (GnRH) pulses and amplitude, frequency, and concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum. In Experiment 1, cows were given pulses of saline (control) or 2 micrograms of GnRH infused i.v. during a 0.1-, 1.25-, 5-, 10-, or 20-min period. Concentrations of LH and FSH during 35 min after GnRH infusion were greater than in control cows (P < 0.01), and FSH concentrations were greater when GnRH infusions were for 10 min or less compared with 20 min. In Experiment 2, the effect of GnRH pulse frequency and dose on LH and FSH concentrations, pulse frequency, and pulse amplitude were determined. Exogenous GnRH (0, 2, or 4 micrograms) was infused in 5 min at frequencies of once every hour or once every 4th hr for 3 d. There was a dose of GnRH x frequency x day effect on LH and FSH concentrations (P < 0.01), indicating that gonadotropes are sensitive to changes in pulse frequency, dose, and time of exposure to GnRH. There were more LH pulses when GnRH was infused every hour, compared with an infusion every 4th hr (P < 0.04). Amplitudes of LH pulses were greater with increased GnRH dose (P < 0.05), and there was a frequency x dose x day effect on FSH pulse amplitude (P < 0.0006). We conclude that LH and FSH secretion in the bovine is differentially regulated by frequency and dose of GnRH infusions.     

Effects of frequency and duration of outdoor exercise on the prevalence of hock lesions in tied Swiss dairy cows

Injuries around the tarsal joint are common in dairy cows kept in tie stalls. This study investigated the influence of the frequency and duration of outdoor exercise on the prevalence of hock lesions in tied Swiss dairy cows. Over a 1-year period (from January to December), cows on 66 farms were examined a total of six times (once every 2 months) for the number and severity of hock lesions (hairless patches, scabs and open wounds, swellings). The prevalence of scabs and wounds (mean 2.1 scabs per cow and farm, range 0.3-4.1) was negatively associated with the duration of outdoor exercise, and positively associated with its frequency. It was also significantly affected by the time of visit and the type of bedding (straw being better than other materials). With increasing length of the lying area, the prevalence of scabs and wounds decreased. Based on the interpretation of the final model, it is suggested that a minimum of 50h spent outdoors over a 4-week period is necessary to have a marked result on the prevalence of hock lesions.     

A free-choice intake of mineral blocks in beef cows during the grazing season and in winter

A herd of 25 beef cows were offered four types of mineral blocks (A, B, C, D) with a different Ca to P ratio (A 0.6:1, B 0.8:1, C 2:1 and D 3.6:1). The Mg content was identical in all blocks whereas the Na content was equal in B, C and D, while the Na content in A block was double. The mineral block intake was monitored for 1 year, which was broken down to the grazing period (Pa) and the winter period (Wi). The intake of pasture grass and winter forage was assessed and the feed chemical composition was analysed; based on the obtained values, a macroelement balance (for Ca, P, Mg, Na and K) was calculated.The results showed the forage diet met requirements for all the observed macroelements (except in Na). The macroelement intake from forage was considerably higher than from mineral blocks. There were significant seasonal (Pa versus Wi) differences in B and C blocks intake. The consumption of D block was relatively invariable all year round; block A was refused in both seasons though it contained the highest amount of highly deficient Na.It can be concluded that mineral content in forage meets beef cattle requirements for Ca, Mg and K, P content is just satisfactory, and Na content is insufficient. It appears that cows control, to some extent, the Ca to P ratio in their diet by choosing the appropriate type of mineral block. However, the preference or refusal of some types of mineral blocks regardless of the season suggests the influence of other factors affecting mineral block intake which were not the subject of our observation.     

Effects of energy supplementation on productivity of dual-purpose cows grazing in a silvopastoral system in the tropics

The aim of the present work was to evaluate milk yield, postpartum (pp) ovarian activity and pregnancy rate in dual-purpose cows grazing Cynodon nlemfuensis and browsing L. leucocephala, with or without energy supplementation. Twenty-four Bos taurus × B. indicus cows were divided in two groups from calving to 70 days post-calving: supplemented group (SG) with ground sorghum grain offered at 0.4% of live weight at calving and control group (CG) without supplement. There was a trend for milk yield (kg day(-1)) to be greater (p = 0.08) for SG (10.55 ± 0.51) compared to CG (9.53 ± 0.61), although without differences in fat (0.42 ± 0.02 vs. 0.38 ± 0.03 kg day(-1)), protein (0.29 ± 0.02 vs. 0.29 ± 0.02 kg day(-1)) or lactose (0.49 ± 0.02 vs. 0.49 ± 0.03 kg day(-1)) concentration. Populations of large, medium and small follicles were similar between treatments. Percentage of cows which showed corpus luteum tended to be greater in SG (50%), compared to CG (33%). Supplemented cows tended to have a shorter calving-first corpus luteum interval (40 ± 10 vs. 51 ± 10 days) and had a significantly higher (χ (2) = 0.03) pregnancy rate (42% vs. 0%). It is concluded that energy supplementation helped to improve ovarian activity and pregnancy rate. Since supplementation did not avoid loss of body condition, the higher pregnancy rate in SG suggests beneficial effects of supplementation probably mediated by metabolic hormones.     

Influence of pasture sward height and concentrate supplementation on intake, digestibility, and grazing time of lactating beef cows

To establish the effect of sward height (SH) and concentrate supplementation on performance of grazing cattle, 24 crossbred Angus beef cows (535 kg BW) and calves (114 kg BW) were grouped by weight and calving date. They were randomly assigned to two SH treatments, either 4 to 8 cm or 8 to 11 cm, and fed three levels of supplement, high, low, or none, consisting of 6.24, 3.12, and 0 kg x animal(-1) x d(-1), respectively. The experiment was repeated over three 15-d periods in 1996: May (P1), June/July (P2), and August (P3). No SH x supplement level x period or SH x supplement level interactions (P > 0.10) were evident for responses tested. Cows on lower SH had greater (P < 0.08) DMI but spent an additional 1.3 h/d (P < 0.01) grazing compared with cows on higher SH. Sward height had no influence (P > 0.10) on forage DM digestibility (DMD). Forage DMI, DMD, and grazing time (GT) decreased (P < 0.05) as supplementation increased. Nonetheless, supplemented cows consumed more total DMI (P < 0.08) than unsupplemented cows. Cows consumed 2.4 kg/d more forage DM (P < 0.01) in P1 and P2 than in P3. Cows grazed 1.3 h/d (P < 0.01) less in P1 than in P2 and P3. Grazing efficiency (DMI/h GT) declined as supplementation increased and grazing season advanced to P3 (P < 0.01). Decreased forage DMI and grazing efficiency with increasing supplementation suggests that supplemented cattle should be able to maintain productivity while grazing at SH lower than unsupplemented cattle.     

Grazing and feedlot performance of yearling stocker cattle integrated with spring- and fall-calving beef cows in a year-round grazing system

Effects of calving season and finishing system on forage and concentrate consumption and carcass characteristics of calves were compared. In each of 3 yr, two replicates of three growing and finishing systems were compared including 1) spring calves finished on a high-grain diet in a feedlot immediately post-weaning (WF); 2) spring calves backgrounded on a hay-corn gluten diet over winter for 179 +/- 18 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (SGF); and 3) fall calves backgrounded on a hay-corn gluten feed diet over winter for 69 +/- 31 d after weaning, grazed for 98 +/- 9 d in cool-season grass-legume pastures, and finished on a high-grain diet in a feedlot (FGF). During the grazing phase, calves on the SGF and FGF treatments were equally stocked with spring-calving cow-calf pairs before grazing by pregnant fall-calving cows in a first-last rotational stocking system at a rate of 1.9 standard livestock units/ha. As designed, retained calves in the FGF system spent 110 fewer days in the drylot during backgrounding than retained calves in the SGF system (P = 0.01), resulting in less feed provided during winter. A greater (P < 0.01) quantity of hay was fed to SGF calves after weaning over winter (1,305 kg of DM per calf) than the quantity fed to FGF calves (305 kg of DM per calf). Quantity of grain (including commercial starter) fed to SGF calves after weaning did not differ (P = 0.28) from that fed to FGF calves (126 vs. 55 kg of DM per calf); however, calves in the FGF system required 80 and 71 kg of DM per calf more concentrate to finish to an equivalent external fat thickness compared with SGF and WF calves, respectively (P = 0.02). Average daily gains in the feedlot were greater (P < 0.01) for SGF and FGF calves than for WF calves during all 3 yr. There were no differences (P = 0.69) in carcass quality grades among calves in all groups, but SGF calves had greater (P < 0.01) hot carcass weight and LM area measurements at slaughter than FGF or WF calves. Although calves in the FGF system were 25 kg lighter than calves in the WF system at slaughter (P = 0.03), and had a lower dressing percent (P = 0.03), other carcass characteristics did not differ between these two groups. Lower stored-feed requirements and similar carcass quality characteristics made retention of a fall calf crop advantageous over retention of a spring calf crop for use as stocker animals before finishing.     

Timing of herbage allocation in strip grazing: Effects on grazing pattern and performance of beef heifers

The timing of grazing bouts (GB) determines how cattle allot time to meet their nutritional needs. Net photosynthesis and evapotranspirational losses increase herbage nonstructural carbohydrate and DM concentrations, which may lead to longer and more intense GB at dusk. Hence, linking the grazing pattern, plant phenology, and herbage allocation time emerges as an option to manipulate the GB and nutrient intake. The objectives of this work were to analyze grazing behavior and performance of beef heifers when herbage allocation was at 0700 each morning (MHA) or at 1500 each afternoon (AHA). Two pairs of experiments were conducted during the winter and spring examining behavior and performance. Measurements were grazing, rumination, and idling times during daylight hours, and their patterns, as well as bite rate, ADG, change in BCS, and daily herbage DMI. In the behavioral experiments, 8 heifers strip-grazed annual ryegrass (Lolium multiflorum Lam.). The grazing, rumination, and idling times as well as bite rate were measured and also analyzed per time of day. In the performance experiments, 48 beef heifers strip-grazed annual ryegrass in 2 groups according to treatments. Daily DMI, ADG, and changes in BCS were analyzed. The AHA increased daily idling time (P < 0.01) and decreased grazing time (P < 0.01). The AHA concentrated grazing time in the evening, when bite rate was greater (P < 0.01). The daylight rumination time varied by time of day (P < 0.01), but total daylight rumination time did not differ (P = 0.11). With AHA, rumination time and idling time were concentrated in the morning and afternoon. In the performance experiment during the winter, there was a treatment x week effect (P < 0.01) for ADG and change in BCS. Beginning in wk 4, heifers in AHA gained 150 g of BW and 0.0145 points of BCS more than those in MHA (P < 0.05) per day. In the spring, AHA increased ADG by 549 g and 0.0145 points of BCS more than those in MHA (P < 0.05) per day during the entire 6 wk. The herbage DMI (kg/d) did not differ in winter (AHA, 5.0 vs. MHA, 4.5) or spring (AHA, 5.6 vs. MHA, 5.0). These results suggest that timing of herbage allocation alters grazing, rumination, and idling patterns; AHA leads to longer and more intense GB when herbage has greater quality, which improves cattle performance.