ABSTRACT:A study was conducted over 3 yr to evaluate effects of sire birth weight EPD, calf birth weight and shape, and heifer pelvic area and weight, individually and in combination, on dystocia and subsequent rebreeding of 2-yr-old heifers. Heifers ( n = 550), MARC II yearlings, were assigned for breeding to one of four Angus sires with birth weight EPD of −.95, −.82, +2.9, and +2.7 kg. At calving, heifers were assisted as needed. A gauge attached to the calf puller recorded applied traction pressure. Analysis of traction pressure detected only slightly larger amounts of variation ( 2 to 3%) affecting dystocia than the standard five-point scoring system. Dam weight did not affect calving difficulty score (CDS), except dam birth weights were heavier ( P < .05) for CDS 5 (Caesarean section) than CDS 1 (unassisted). Dams requiring Caesarean section had smaller pelvic areas ( P < .05), with no other differences among CDS. The CDS increased as calf birth weight and calf external measurements increased. Low EPD sires produced calves with smaller ( P < .05) birth weights and smaller calf head and foot circumferences and caused less dystocia than high EPD sires. The CDS did not affect subsequent pregnancy rates but did affect conception date of the second calf. Calves delivered by Caesarean section were lighter ( P < .05) at weaning than other calves but had similar slaughter weights. As mean winter temperature increased (6.1°C ) from yr 1 to 3, calf birth weight decreased (4.6 kg) and calving difficulty decreased 23%. Results indicate sire birth weight EPD, calf birth weight and shape, dam pelvic area, and climate affected CDS, and CDS affected subsequent conception date.

The objective of this study was to determine whether a combination of Cu, Co, Mn, and Zn in an organic or inorganic form fed at higher than nutrient recommendations for 2-yr-old cows from calving to breeding would affect pregnancy rate, calving date, calf performance, and cow liver and serum mineral concentrations. Crossbred 2-yr-old cows were used after calving in 1994 (n = 127) and 1995 (n = 109). Cows were blocked by calving date to one of three treatments: 1) no supplemental minerals (CTL), 2) organic minerals (ORG), or 3) inorganic minerals (ING). Minerals were fed for the same daily intake for both organic and inorganic treatments: Cu (125 mg), Co (25 mg), Mn (200 mg), and Zn (360 mg). Cows were individually fed a mineral-protein supplement with grass hay from calving (February-March) to before breeding (May 15). Hay intakes were calculated using chromium oxide boluses to determine fecal output. Fecal excretion of minerals was calculated following trace element analysis of feces. Liver biopsies were obtained before calving, after calving (start of supplementation), at the end of supplementation, and in midsummer. Over 2 yr, more cows did not become pregnant (P < .01) in ORG (11/78) and ING (11/78) treatments than in CTL (0/80) treatments. A treatment x year interaction was found for day of conception. Cows in the ORG group conceived later (P < .01) than cows in the ING or CTL groups in 1994. In 1995, there was no difference (P > .10) in day of conception among groups. Liver Zn and Mn concentrations were not different (P > .10) and Cu concentrations increased (P < .01) for the ORG and ING groups. Cows in the ORG and ING groups had higher (P < .01) concentrations of Cu, Mn, and Zn in the feces than the CTL cows. Trace elements in the feces did not differ for ORG and ING groups. Results indicate that combinations of Cu, Co, Mn, and Zn fed at higher levels than are required reduced reproductive performance.

Two trials were conducted to evaluate effects of Synovex C implants on replacement heifers, given at two different ages. Crossbred heifer calves (n = 370) were allotted to four treatments: 1) nonimplanted controls, 2) implanted at 2 mo, 3) implanted at 6 mo, and 4) implanted at both 2 and 6 mo of age. Heifers implanted at 2 mo gained 7 kg more (P = .01) by 6 mo than those not implanted at 2 mo. No differences were found in 22-mo weights. All implanted heifers had larger (P = .01) yearling pelvic area than controls. All heifers implanted at 6 mo continued to have larger (P = .01) pelvic area at 22 mo. All implanted heifers had higher (P = .05) occurrence of non-ovulatory estrus. No differences were found among treatments in percentage of heifers puberal before breeding, in estrus first 21 d of breeding, or in first-service conception rate. In only one trial, pregnancy first 21 d and total pregnancy in 63-d breeding season were decreased (P = .05) by implanting at 6 mo. At subsequent calving, an interaction existed between the effects of the 2- and the 6-mo implant for calf birth weight and pelvic area:birth weight ratio. A single implant at either 2 or 6 mo decreased (P = .01) calving difficulty score; and implanting at both 2 and 6 mo showed the greatest reduction in calving difficulty. Implants had no significant long-term effects on reproduction or calf production of 2-yr-old cows.(ABSTRACT TRUNCATED AT 250 WORDS)

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