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Cool-season annual forages provide high-quality herbage for up to 5 mo in the US Gulf Coast states, but their management in pasture-based dairy systems has received little attention. Objectives of this study were to evaluate pasture and animal responses when lactating Holstein cows (n = 32, mean DIM = 184 ± 21) grazed either N-fertilized rye (Secale cereale L.)-annual ryegrass (Lolium multiflorum Lam.) mixed pastures or rye-annual ryegrass-crimson clover (Trifolium incarnatum L.)-red clover (Trifolium pratense L.) pastures at 2 stocking rates (5 vs. 2.5 cows/ha) and 2 rates of concentrate supplementation [0.29 or 0.40 kg of supplement (as is)/kg of daily milk production]. Two cows paired by parity (one multiparous and one primiparous) were assigned randomly to each pasture. The 2 x 2 x 2 factorial arrangement of treatments was replicated twice in a completely randomized design. Forage mixture and supplementation rate did not affect milk production during three 28-d periods. Greater milk production occurred at the low (19.7 kg/d) than the high (14.7 kg/d) stocking rate during periods 2 and 3, but production was similar during period 1. Despite lower production per cow, milk production per hectare was generally greater at the high stocking rate (81.6 vs. 49.5 kg/ha). Generally, greater pregraze herbage mass on pastures at the lower stocking rate (1,400 vs. 1,150 kg/ha) accounted for greater herbage allowance. Both forage (8.0 vs. 5.9 kg/d) and total (14.1 vs. 11.6) organic matter intake were greater at the low stocking rate. Cows fed less supplement had greater forage organic matter intake (8.0 vs. 6.1 kg/d). Greater herbage mass was associated with the greater intake and subsequent greater milk production. Differences in forage nutritive value, blood metabolites and milk composition, although showing some response to treatments, may not be of sufficient magnitude to affect choice of pasture species or other management practices. Animal performance was not improved by adding clovers to mixed cool-season grass pastures like those in this study. Stocking rate had a major effect on pasture and animal performance. During the cool season, supplementation with concentrates should be planned based on estimated energy intake from forages to achieve optimum milk production and ensure maintenance of body condition. [ABSTRACT FROM AUTHOR]

The objective was to compare productive and metabolic responses of lactating dairy cows managed on 2 pasture-based systems using a concentrate supplement (n = 16) with those of a freestall housing system (n = 24). In a 259-d experiment, 3 multiparous Holstein cows were assigned at calving to each of 4 replicates of 2 pasture systems. For system 1, winter pastures were a mixture of rye, ryegrass, and crimson and red clover; summer pastures were pearl millet. Pasture system 2 included a rye-ryegrass mixture during winter and bermudagrass during summer. Pregraze herbage mass averaged 2.3 and 3.6 Mg/ha for winter and summer pastures, respectively; however, during August through September, pearl millet pregraze mass was reduced to about 1 Mg/ha. Daily dry matter intake by cows on pasture averaged 24.7 kg/d in winter and 19.0 kg/d in summer, of which 55% was from pasture; that of cows in confined-housing averaged 23.6 kg/d. Cows in confinement produced 19% more milk (29.8 vs. 25.1 kg/d) than those on pasture systems. Differences in concentration of milk fat, protein, or urea N were not detected among treatment groups. Grazing cows lost more body weight than confined cows (113 vs. 58 kg) and had lower concentrations of plasma glucose in the early weeks postpartum. Despite greater milk yield by cows housed in freestalls, milk income minus feed costs including that of pasture was similar for the 3 management systems. Although these pasture systems might be a viable management system in the southeastern US, extensive loss of body weight immediately postpartum for pasture-based cows are a potential concern. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays a critical role in the sustainability of grazingland ecosystems around the world. However, maintaining or increasing SOC levels remains a major challenge, particularly in subtropical regions where coarse-textured soils predominate. This study evaluated the long-term (>20 years) impacts of grazingland intensification (conversion of native rangelands into more intensively managed silvopasture and sown pasture) on SOC and nitrogen (N) responses in particle size/density fractions. Treatments consisted of field replicated (n = 2) experimental sites that represented a gradient of intensification ranging from native rangelands (low intensification), pine (Pinus spp.)-bahiagrass (Paspalum notatum) silvopasture (moderate intensification), and bahiagrass pastures (high intensification). Soil organic C and N increased in response to the conversion of native rangelands into more intensively managed grazinglands, but no difference was observed in total SOC and N between silvopasture and sown pasture. Despite the positive impact of intensification on SOC and N pools, accumulation occurred primarily in more labile fractions. For instance, at the 0 to 10 cm depth, light-free C (LF-C) increased from 12.9 g kg−1 soil in the native rangeland to 24.7 g kg−1 soil in the sown pasture. Largest differences between the ecosystems were observed at the 10 to 20 cm depth where LF-C increased by as much as 170% following the conversion from native rangelands to sown pasture. Similar responses were also observed for N. Grazingland intensification showed no effect on soil aggregation, but SOC and N associated with macroaggregates (2,000 to 250 μm) increased with intensification. Results indicate that grazingland intensification promoted SOC and N accumulation, primarily through an increase in the LF fraction. [ABSTRACT FROM AUTHOR]

The objective of this trial was to investigate the effects of feeding a soybean oil refining by-product (SORB), made up mainly of sodium salts of long-chain fatty acids, on reproductive performance and productivity of 36 early lactation Holstein cows managed in a free-stall barn or on annual rye-ryegrass pasture. In this 2 x 2 factorial arrangement of treatments, cows consumed 0 or 0.5 kg/d of SORB as part of a total mixed ration for barn cows or as part of a grain supplement fed to cows on intensively, rotationally stocked pasture. Blood was sampled 3 times weekly and plasma was measured for progesterone to assess ovarian activity. Estrus activity was recorded using the HeatWatch estrus detection system. Although average 14-wk milk production (37.2 kg/d) was not different among treatments, barn cows had more persistent lactations than did grazing cows. Cows housed in the barn lost less body weight and returned to initial body weight sooner and had lower mean concentrations of plasma nonesterified fatty acids (464 vs. 261 mEq/L) than those managed on pasture. The milk fat of cows on pasture contained greater proportions of conjugated linoleic acid and linolenic acid but a corresponding 0.22 percentage unit decrease in milk fat concentration (3.39 vs. 3.16%). Cows managed on pasture had greater peak concentrations of plasma progesterone during the first estrous cycle. Cows managed on pasture and fed SORB had the greatest accumulation of plasma progesterone over the 14 wk of the study (SORB x housing interaction). These cows experienced the most mounts during their first estrus (9.3) and pregnancy rate was also greatest for this treatment (62.5%). Feeding SORB did not affect production of milk, fat, or protein. Loss of body condition was less in cows fed SORB. Ruminal fluid concentration of propionate increased and ruminal pH decreased in cows fed SORB. A lower proportion of fatty acids less than 18 carbons in length was found in the milk fat of cows fed SORB, thus indicating lower de novo synthesis of fatty acids. Higher proportions of C18:2n-6 and conjugated C18:2 were found in the milk fat of cows fed SORB. Based on concentrations of plasma progesterone, cows fed SORB experienced their first ovulation earlier (26.7 vs. 42.4 d postpartum) than did cows not supplemented with SORB. Neither housing system nor SORB supplementation influenced detection of first estrus (50.5 d) or the mean length of each estrus period (447 min). [ABSTRACT FROM AUTHOR]

Objectives were to evaluate effects of forage species, stocking rate, and supplementation rate on performance and physiology of grazing lactating Holstein cows under intensive rotational stocking management during summer. Eight treatments were arranged in a 2 x 2 x 2 factorial design. Animals (n = 62) grazed pastures of Tifton 85 bermudagrass or Florigraze rhizoma peanut, a tropical legume. Low and high stocking rates were 7.5 and 10.0 cows/ha for bermudagrass and 5.0 and 7.5 cows/ha for rhizoma peanut. Within each forage-stocking rate combination, cows were fed supplement at 0.33 or 0.5 kg of supplement (as-fed basis)/kg daily milk production. Cows grazing rhizoma peanut pastures produced more milk (16.9 vs. 15.4 kg/d) but had higher rectal temperatures (39.4 vs. 39.1 degrees C). Milk production per cow was improved at the higher stocking rate for bermudagrass but was reduced at the higher stocking rate for peanuts. Increasing supplementation rate boosted plasma glucose, milk production, and milk protein percent. Increased supplementation rate had a greater positive impact on milk production of cows grazing bermudagrass compared to rhizoma peanut (21.9 vs. 10.6% increase) due to a lower substitution of grain for forage intake. Organic matter intakes of forage, supplement, and total diet were greatest by cows grazing rhizoma peanut pastures and averaged 12.4, 6.1, and 18.5 kg/d compared to 9.2, 5.4, and 14.6 kg/d for cows grazing bermudagrass. Despite lower individual feed intake and performance, production per unit land area was 29% greater (112 vs. 90 kg of milk/ha per d) for cows grazing bermudagrass due to the greater stocking rate possible with that forage. Only cows supplemented at the high rate and kept at the high stocking rate on bermudagrass maintained body weight. Cows on other treatments lost body weight. Tifton 85 bermudagrass appears to be an excellent summer forage for dairy cows grazing in the southeastern U.S. given its nutritive value characteristics and high yields. Optimum stocking rate may be as high as 10 cows/ha during times of peak growth of forage for low-to-moderately producing cows fed supplement. Furthermore, the positive milk production response to additional supplement when cows grazed Tifton 85 pastures (0.8 kg/kg of supplement), indicates the value of providing supplement to cows grazing this moderate quality forage.

This experiment tested performance and physiological responses to evaporative cooling, bovine somatotropin (bST), and supplemental silage of lactating cows grazing bermudagrass (Tifton 85; Cynodon dactylon x C. nlemfuensis cv.) pastures. Multiparous (n = 32) cows (196 d in milk) were assigned one of five treatments arranged in two replicates. Treatments were 1) cows maintained continuously on pasture with access to shade, 2) treatment 1 + bST, 3) night housing on pasture, then free-stall housing with fans and misters from 0730 to 1630 h, 4) treatment 3 + bST, and 5) treatment 4 + corn silage fed at 0.5% of body weight (dry matter basis) in the barn. A grain supplement was fed at a rate of 0.5 kg/kg of milk produced. Time spent grazing ranged from 4 to 7.2 h/d, with cows fed corn silage spending the least amount of time. Cows given bST grazed 45 min/d longer than controls, but intake of bermudagrass was unchanged. Intake of bermudagrass ranged from 7.4 to 9.5 kg/d of organic matter, with the lowest intake by cows fed corn silage. With the exception of cows fed corn silage, cows kept in a cooling barn during the day ate equivalent amounts of pasture as those given unlimited access to pasture. Production of 4% fat-corrected milk was greater by cows injected with bST (17.7 vs. 15.8 kg/d) compared with controls and tended to be greater for cows given daytime cooling compared with cows on pasture continuously (17.2 vs. 16.3 kg/d). Cows provided evaporative cooling did not lose weight compared with continually pastured cows (6.3 vs. -10.9 kg/24 d). Cows injected with bST compared with controls maintained their body weight better (2.5 vs. -7.1 kg/24 d). Cows given bST had increased concentration of plasma insulin-like growth factor-I (142 vs. 89 ng/ml), insulin (0.60 vs. 0.56 ng/ml), and nonesterified fatty acids (318 vs. 239 mEq/L). Cows given bST and those continually on pasture had greater diurnal body temperatures. Use of barn cooling systems and bST treatments as management tools provided limited improvement in performance of midlactation cows managed in pasture-based systems.

'Mott' dwarf elephantgrass, forage sorghum, 'Tifton 81' bermudagrass, and whole corn plant were stored as silage and fed as the only forage source in diets formulated to 31, 35, and 39% NDF. The 12 diets were fed for ad libitum intake as a TMR to midlactation Holstein cows, primarily to determine the effect of NDF concentration and forage source on DMI and milk production. Increased dietary NDF concentration linearly decreased DMI (3.69 to 3.35%) and OM intake (3.39 to 3.06%) as a percentage of BW and linearly increased NDF intake as a percentage of BW (1.15 to 1.32%). Production of milk (23.0 to 21.7 kg/d) and 4% FCM (20.7 to 19.6 kg/d) and percentage of milk protein (3.16 to 3.07%) decreased linearly as dietary NDF concentration increased. Cows fed dwarf elephantgrass silage or corn silage, which were higher quality forage sources based on greater rates and extents of fiber digestion, consumed more DM and produced more milk than cows fed sorghum silage or bermudagrass silage. Cows fed diets containing sorghum silage had the lowest DMI and milk production. Apparent digestibility of NDF and ADF from corn silage and dwarf elephantgrass silage was greater than that of sorghum silage and bermudagrass silage. In addition to dietary NDF concentration, digestibility of dietary fiber influences DMI and milk production.

During 1990 and 1991, pastures of 'Callie' bermudagrass [Cynodon dactylon (L.) Pers.] located near Gainesville, FL (29 degrees 60' N latitude) were used to determine the effects of three grazing methods on performance of 250-kg Holstein heifers (Bos taurus) and forage nutritive value and botanical composition. The grazing methods were rotational stocking (15 paddocks) with short grazing periods (1.5 to 2.5 d/paddock), rotational stocking (three paddocks) with long grazing periods (10 to 14 d/paddock), and continuous stocking. Average daily gain across years did not differ among methods (.50 +/- .04 kg), partially because average in vitro digestible OM concentration of herbage varied little (558 +/- 12 g/kg of OM). Across years, rotational stocking with short grazing periods had a greater average stocking rate (3520 kg of liveweight/ha per d) than did rotational stocking with long grazing periods (2980 kg/ha per d), but no differences occurred in heifer gain among the three grazing methods (697 +/- 30 kg/ha). Under the conditions of our 2-yr study, effect of grazing method on heifer performance was slight, but the potential for long-term differences exists because 'Callie' stand longevity is greater under rotational stocking.