Jeremy L. Martin

Winter grazing system and supplementation during late gestation influence performance of beef cows and steer progeny

ABSTRACT A 2 × 2 factorial study evaluated effects of cow wintering system and last trimester CP supplementation on performance of beef cows and steer progeny over a 3-yr period. Pregnant composite cows (Red Angus × Simmental) grazed winter range (WR; n = 4/yr) or corn residue (CR; n = 4/yr) during winter and within grazing treatment received 0.45 kg/d (DM) 28% CP cubes (PS; n = 4/yr) or no supplement (NS; n = 4/yr). Offspring steer calves entered the feedlot 14 d postweaning and were slaughtered 222 d later. Precalving BW was greater (P = 0.02) for PS than NS cows grazing WR, whereas precalving BCS was greater (P < 0.001) for cows grazing CR compared with WR. Calf birth BW was greater (P = 0.02) for CR than WR and tended to be greater (P = 0.11) for PS than NS cows. Prebreeding BW and BCS were greater (P ≤ 0.001) for CR than WR cows and PS than NS (P = 0.006) cows. At weaning, CR cows were heavier (P < 0.001) than WR cows but had similar BCS (P = 0.74). Cow weaning BW and BCS were not affected (P > 0.32) by PS. Calf weaning BW was less (P = 0.01) for calves from NS cows grazing WR compared with all other treatments. Pregnancy rate was unaffected by treatment (P > 0.39). Steer ADG, 12th-rib fat, yield grade, and LM area (P > 0.10) were similar among all treatments. However, final BW and HCW (P = 0.02) were greater for steers from PS-WR than NS-WR cows. Compared with steers from NS cows, steers from PS cows had greater marbling scores (P = 0.004) and a greater (P = 0.04) proportion graded USDA Choice or greater. Protein supplementation of dams increased the value of calves at weaning (P = 0.03) and of steers at slaughter regardless of winter grazing treatment (P = 0.005). Calf birth and weaning BW were increased by grazing CR during the winter. Calf weaning BW was increased by PS of the dam if the dam grazed WR. Compared with steers from NS cows, steer progeny from PS cows had a greater quality grade with no (P = 0.26) effect on yield grade. These data support a late gestation dam nutrition effect on calf production via fetal programming.

Winter grazing system and supplementation of beef cows during late gestation influence heifer progeny

A 2 × 2 factorial arrangement of treatments was used to evaluate effects of dam winter grazing system and supplementation in the last third of gestation on subsequent BW gain, feed efficiency, and reproduction in heifer progeny. Crossbred cows (yr 1, n = 109; yr 2, n = 114; yr 3, n = 116) grazed range (WR) or corn residue (CR) during winter and within grazing treatment received 0.40 kg/d of 31% CP (DM basis) cubes (PS) or no supplement (NS). Heifer calves (yr 1, n = 56; yr 2, n = 56; yr 3, n = 54) grazed dormant pasture for 114 d postweaning and were individually fed for 87 d before a 45-d natural service breeding. Dam PS reduced (P = 0.04) heifer birth date and CR tended to increase (P = 0.07) heifer birth BW. Both PS and CR increased (P ≤ 0.05) heifer weaning BW; however, adjusted 205-d weaning BW was only lighter (P = 0.03) if the dam grazed WR with NS. Heifers from PS dams tended to be younger (P = 0.09) at puberty than NS, and there was a trend (P = 0.11) for more heifers to be pubertal by breeding if the dam grazed WR with PS compared with other treatment groups. Heifers from WR-NS dams tended to weigh less (P ≤ 0.09) at breeding and at pregnancy diagnosis than WR PS. There was a trend (P = 0.13) for pregnancy rate to be greater for heifers born to PS dams. Individually fed heifer DMI was not affected (P = 0.25) by treatment; however, heifers from dams that grazed CR with PS gained the least BW (P = 0.04) during individual feeding and had the smallest (P = 0.03) G:F. In contrast, there were no differences (P > 0.15) in feed efficiency when expressed as residual feed intake. The first calf birth and weaning BW of the heifer was unaffected (P > 0.15) by dam treatment. Heifers from dams that grazed WR with NS tended to have lighter (P = 0.09) BW before the second breeding season but similar (P = 0.97) pregnancy rates. Cows grazing CR with NS produced the most valuable heifer calf at weaning; however, heifers from cows that grazed WR with NS cost the least to develop per pregnant heifer. Winter grazing system and late gestation supplementation affected heifer progeny BW, feed efficiency, and fertility.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Nutritional aspects of developing replacement heifers 1

Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.

The effects of supplementing beef cows grazing cornstalk residue with a dried distillers grain based cube on cow and calf performance1

ABSTRACT Multiparous beef females (n = 832) were used to study the effects of supplementing cows grazing cornstalk residue with a dried distillers grain based cube on cow and calf performance. Cows were blocked by age, BCS, BW, and calving date and assigned randomly to 1 of 2 treatments: 1) supplemented with protein and energy using a dried distillers grain based cube or 2) not supplemented (control) during the last trimester of pregnancy. Cow BW was similar at initiation and at the end of cornstalk grazing, and at the initiation of the breeding season. Supplementation did not affect BCS at the start of breeding (5.4 ± 0.1) or at the initiation of cornstalk grazing the subsequent year. Body condition score of supplemented cows was greater (P = 0.02) at the end of cornstalk grazing compared with that of control cows (5.6 vs. 5.4 ± 0.1). Calving interval, calf birth weight, and calf weaning weight were not different. Percentage of cows cyclic before breeding and final pregnancy rates did not differ. Heifer progeny (n = 306) retained as replacements were similar in initial weight (277.5 ± 10.2 kg), final weight (351 ± 11.5 kg), initial and final BCS, and ADG (0.45 ± 0.04 kg/d). Age at puberty, response to synchronization, AI conception and pregnancy rates, and final pregnancy rates were not different. Supplementation of a dried distillers grain based cube to cows grazing cornstalks improves BCS in the last trimester without affecting reproduction, calf performance, or reproductive performance of heifer progeny.

Effect of dietary crude protein source on hormone and follicle characteristics in beef heifers

Ground, raw soybeans (SB), or dried distillers grain plus solubles (DDGS) were utilized in heifer development diets to determine the effect of dietary fat and protein source on hormone and follicle characteristics and ADG. The experiment was conducted over 2 yr with 100 June-born heifers (199 +/- 2 kg initial BW, n = 50 per yr). The experimental periods were 157 and 207 d in yr 1 and 2, respectively. Heifers were provided a dietary supplement (DM basis) of 1.23 kg of SB and 0.40 kg of corn or 1.65 kg of DDGS between weaning and breeding. Estrus was synchronized with 2 injections of PGF(2alpha) 14 d apart. Dominant follicles were measured and aspirated via transvaginal ultrasonography 60 h after the second PGF(2alpha) injection. Heifers were exposed to bulls beginning 14 d after aspiration for 45 d. Heifer ADG was greater (P = 0.02) for DDGS heifers in yr 1, but was similar (P = 0.47) in yr 2. However, there was no difference (P = 0.35) in final BW in either year. There was no difference (P >or= 0.67) in follicle size, follicle hormone concentrations, or pregnancy rate (88%) between yr 1 and 2. Serum estrogen at 48 or 60 h after PGF(2alpha) injection were similar (P >or= 0.91); however, LH at 60 h in yr 2 tended to be greater (P = 0.07) for DDGS heifers. The percentage of heifers experiencing an LH surge 48 and 60 h after PGF(2alpha) injection was not affected (P >/= 0.40) by treatment. Calf production was not affected (P >or= 0.20) by developmental diet. In summary, DDGS and SB have similar effects on hormone and follicle characteristics at the inclusion rates used in these studies.