Effects of short-term nutritional increase before artificial insemination on average daily gain and reproductive efficiency in March-calving beef heifer development systems

Objective

Our objective was to evaluate increased nu- tritional energy before AI on BW, ADG, and reproductive efficiency in heifers developed on range or in a drylot.

Materials and Methods

A 3-yr study used Angus crossbred heifers (n = 100/yr) near North Platte, Nebras- ka. Heifers were stratified by BW and assigned to 1 of 3 treatments. During winter development (131 ± 3.5 d/yr), heifers grazed upland range (RANGE) or were fed a drylot diet in 2 pens with a targeted gain of 0.68 kg/d to achieve 65% of mature BW (6.35 kg/head per day hay, 2.27 kg/ head per day wet corn gluten feed, and 0.34 kg/head per day supplement). Thirty-three days before AI, one dry- lot group remained on this diet (DLLO) while the other (DLHI) received an additional 4.08 kg/head per day wet corn gluten feed. Heifers developed on RANGE received 0.45 kg/head per day of a 29% CP, dried distillers grain– based pellet until 38 d before AI, when they were fed the DLLO diet.

Results and Discussion

Prebreeding BW was great- er for DLHI (375 ± 3.4 kg) and DLLO (363 ± 3.4 kg) compared with RANGE (312 ± 3.4 kg), but breeding ADG was greater for RANGE (0.69 ± 0.01 kg) compared with DLHI (0.35 ± 0.02 kg) and DLLO (0.37 ± 0.02 kg). Pregnancy rates to AI were similar among DLHI (69%), DLLO (63%), and RANGE (49%); final pregnancy rates tended to be different: DLHI (96%), DLLO (95%) and RANGE (84%). Calving rate and calving in the first 21 d was similar.

Implications and Applications

Greater nutrient and energy intake for DLHI and DLLO led to greater BW and ADG compared with RANGE, but short-term nutri- tional increase had no effect on pregnancy rate to AI nor final pregnancy rates.