D. D. Buskirk

The influence of processed corn and supplemental fat on digestion of limit-fed diets and performance of beef cows.

Trial 1, 135 crossbred cows with calves were used to compare limit-fed corn-hay diets with ad libitum hay and cracked with whole corn in limit-fed diets. Diets were to supply similar TDN intakes. Cow-calf pairs were fed treatment diets from 24 h after parturition until the beginning of the breeding season (62+/-13 d). Cow and calf performance was not affected (P > .05) by intake level or corn processing. In Trial 2, 48 crossbred primiparous cows with calves were used to determine the effect of adding 4% fat to a limit-fed corn-hay diet. Diets were to provide similar TDN intakes. Cow-calf pairs were fed treatment diets from 24 h after parturition until the breeding season started (79+/-14 d). Cow weight, condition score change, and calf gain were not affected (P > .05) by supplemental fat. Milk yield and composition were not different (P > .05) 52 d postpartum. At 92 d postpartum, milk production was 65% greater (P = .01) for cows that received supplemental fat. In Trial 3, four cannulated steers were used to evaluate the influence of corn processing and fat supplementation on digestion. Feeding cracked corn improved (P < .05) DM and OM digestion compared with whole corn. Adding 4% supplemental fat did not influence (P > .05) digestion. Limit-feeding a corn-hay diet is an alternative to feeding ad libitum hay that can accomplish similar cow and calf performance. Supplementation of 4% fat can be used in a limit-fed diet without detrimental effects on digestion, lactation, or cow and calf performance.

Differentiation of bovine intramuscular and subcutaneous stromal-vascular cells exposed to dexamethasone and troglitazone

The objectives of these experiments were to compare differentiation of bovine stromal-vascular (S-V) cells isolated from i.m. and s.c. adipose tissues in response to a glucocorticoid and a peroxisome proliferator-activated receptor gamma agonist. Stromal-vascular cells were isolated from i.m. and s.c. fat depots of 3 Angus steers and propagated in culture. Cells were exposed to differentiation media containing 0.25 microM dexamethasone (DEX), a glucocorticoid analog, and 40 microM troglitazone (TRO), a peroxisome proliferator-activated receptor gamma agonist, or both. Cells treated with DEX and TRO had greater (P < 0.02) glycerol-3-phosphate dehydrogenase activity than control cells. No interactions between DEX, TRO, and depot (P > 0.59) or depot differences (P = 0.41) in glycerol-3-phosphate dehydrogenase activity were found. Morphological assessment of adipogenic colonies showed that DEX induced a 1.8-fold increase in the percentage of adipogenic colonies (P = 0.03), whereas TRO increased the proportion of adipogenic colonies by 1.9-fold (P = 0.02) compared with those not treated with DEX or TRO, respectively. Depots had a similar percentage of adipogenic colonies (P = 0.18); however, the percentage of differentiated cells within adipogenic colonies was found to be 6.4-fold greater in s.c. isolates compared with i.m. (P < 0.001). Addition of TRO increased the proportion of differentiated cells within colonies by 10-fold compared with those of nontreated colonies (P < 0.001), whereas the percentage of differentiated cells within adipogenic colonies only tended to be increased by DEX (P = 0.10). These data indicate that bovine i.m. and s.c. S-V cells are capable of enhanced differentiation in response to DEX and TRO, and these effects were additive. Most importantly, inherent differences in the capacity to differentiate exist between adipogenic bovine i.m. and s.c. S-V cells.

Bovine intramuscular, subcutaneous, and perirenal stromal-vascular cells express similar glucocorticoid receptor isoforms, but exhibit different adipogenic capacity.

Understanding preadipocyte differentiation in economically important adipose depots will facilitate efforts to selectively increase intramuscular (i.m.) lipid accretion in cattle. The objectives of this study were to determine if glucocorticoid receptor (GR) expression differs among bovine stromal-vascular (S-V) cells derived from i.m., subcutaneous (s.c.), and peri-renal (p.r.) adipose tissue, and to evaluate the effects of dexamethasone (DEX) on adipogenesis of these cell populations. Stromal-vascular cells isolated from i.m., s.c., and p.r. adipose tissues of 2 steers were propagated in culture and exposed to 0 or 250 nM DEX for 48 h. Cell lysates were subjected to GR immunoblot analysis, and immunoreactive protein bands of approximately 97, approximately 62, and approximately 48 kDa were detected and expressed relative to beta-actin immunoreactivity. The abundance of each GR immunoreactive protein was similar among S-V cell populations (P > 0.50). Dexamethasone exposure decreased the abundance of the approximately 97 and approximately 62 kDa GR immunoreactive bands in S-V cells from the 3 depots (P < 0.001), but did not affect the expression of the approximately 48 kDa band (P = 0.96). Stromal-vascular cells isolated from 3 steers were grown in culture, and upon confluence, were exposed to 0, 25, or 2,500 nM DEX for 48 h. After an additional 10 d in differentiation media, differentiation was determined by glycerol-3-phosphate dehydrogenase (GPDH) specific activity and oil red O staining. The extent of differentiation differed by depot (p.r. > s.c. > i.m.; P < 0.05). Compared with control, 2,500 nM DEX increased GPDH activity in S-V cells from all depots (P < 0.05), and no interaction between depot and DEX concentration was observed (P = 0.99). We observed an adipose tissue depot by DEX concentration interaction (P = 0.03) for S-V cells with large (> or = 10 microm-diameter) lipid droplets. The percentage of p.r. S-V cells with large lipid droplets increased in response to DEX in a linear manner (P < 0.02), but only increased greater than control in s.c. cells exposed to 2,500 nM DEX (P = 0.002). Dexamethasone did not significantly increase the percentage of i.m. S-V cells with large lipid droplets (P > 0.27). Collectively, these data demonstrate differences in adipogenic activity among bovine i.m., s.c., and p.r. S-V cells, but indicate no relationship between adipogenic activity and glucocorticoid receptor abundance or function.

Intensive Grazing Management of Smooth Bromegrass With or Without Alfalfa or Birdsfoot Trefoil: Heifer Performance and Sward Characteristics

Abstract Over 3 yr, 324 (n=108 per yr) Holstein heifers (226±26 kg; ±SD) ranging in age from 5 to 7 mo were assigned to a 3×2 factorial arrangement of treatments to determine the effects of forage and grazing management system on animal performance, forage availability, and forage quality. The forage treatments were: 1) alfalfa and smooth bromegrass (ALF-BR), 2) birdsfoot trefoil and smooth bromegrass (BFT-BR), or 3) smooth bromegrass plus nitrogen (BR). The grazing management systems were: 1) a four-paddock system in which cattle were rotated based on time (4-p) or 2) a 12-paddock system in which cattle were rotated based on forage availability (12-p). Stocking rate was held constant at 3.75 animals per hectare. The ALF-BR and BR pastures yielded more available forage than BFT-BR pastures (9.86 and 10.04 vs 9.14 metric tons/ha). The ALF-BR and BFT-BR pastures, when compared to BR pastures, supported greater animal average daily gain (0.93 and 0.97 vs 0.83 kg/d) and increased animal gain per hectare (497.8 and 516.4 vs 443.3 kg/d). Legume-grass pastures also had lower neutral detergent fiber content than BR pastures. There were no differences in either animal gain or gain per hectare due to grazing system. Three years after seeding, BFT-BR and ALF-BR had a similar percentage of legume present within their respective pastures. Birdsfoot trefoil appears to be an acceptable substitute for alfalfa in properly managed grass-legume mixed pastures.

Subsequent Productivity of Beef Heifers That Received Creep Feed for 0, 28, 56, or 84 d Before Weaning

Abstract Ninety Angus x Hereford rotational cross cows and their backcross heifer calves were used to evaluate the effects of length of time receiving creep feed on subsequent heifer fertility and milk production. Heifer calves (156 ± 16 d of age) were randomly assigned to receive creep feed for 0, 28, 56, or 84 d before weaning while nursing dams grazing endophyte-infected tall fescue, red clover pastures. All heifers were managed alike after the 84-d treatment period. Increasing the length of time receiving creep feed increased rate of gain by 0.33 kg/d when the heifers had access to creep for 84 d compared to controls (linear, P

Comparison of Beef Cattle Performance and Forage Characteristics for Alfalfa or Tall Fescue-Red Clover in a Rotational Grazing System

Cow-calf performance and diet composition were compared between established alfalfa and tall fescue-red clover pastures in a rotational grazing system. Eighty cow-calf pairs were randomly allotted to the two dietary mixtures with three replications. Each of the six pastures was subdivided using a six-paddock rotation so that the paddocks were grazed for 6 d and rested for 30 d throughout the 121-d trial. Put-and-take animals were used to evaluate stocking rate. One ruminally fistulated cow was used in each of the six pastures to determine composition of grazed forage from reticulorumen evacuation at the beginning and end of grazing in paddock 1 (on d 0, 6, 36, 42, 72, 78, 108 and 114). Both treatments sustained similar stocking rates. Cow gain and body condition score change were not different due to treatments (P>0.10). However, weight gains of calves grazing alfalfa were 11.5% higher (P<0.05) than those of calves grazing tall fescue-red clover. Calf gain per hectare for the alfalfa pastures also tended to be higher (P=0.15) than that for tall fescue-red clover. This was due to the improved calf performance on alfalfa with similar stocking rates. Alfalfa was lower in NDF and ADF (P<0.05), and higher in CP at the beginning of grazing (P<0.05). After grazing, alfalfa was lower in NDF and higher in CP (P<0.05). Both alfalfa and tall fescue-red clover effectively maintained cow performance, whereas the alfalfa resulted in improved calf gain.