Impacts of sexed semen utilization on commercial beef production

Abstract

The objectives of this study were to: 1) determine if use of sexed semen adversely affects fertility and embryo viability, and if current sexing technology indeed alters the sex ratio in beef cattle; 2) evaluate the impacts of sexed semen utilization on the biological efficiency of commercial beef production when calves are sold at weaning versus retained through stocker and feedlot phases of production; and 3) determine the economic value of a sexed semen inseminate in commercial beef production when calves are sold at weaning. The first phase of the project involved field trials performed to evaluate the effects of sexed semen use on fertility and embryo viability as well as the efficacy of sexing in skewing the sex ratio. During the 1997 through 1999 breeding seasons, 118. 82. and 123 heifers were bred to control semen, sorted 5° C or 18° C semen, and frozen, sorted semen, respectively. In 1998 and 1999. 121 cows were bred to control semen. 56 cows were bred to sexed 18° C semen, and 140 cows were bred to frozen, sorted semen. Semen from ten Angus bulls of unknown fertility was collected by artificial vagina, processed, stained with the DNA-binding dye Hoechst 33342. and sorted with a 150 mW UV argon laser on a MoFlo® flow cytometer/cell sorter modified for sperm sorting operating at 50 psi using 2.9% Na citrate as sheath fluid in the first two years and a tris buffer in the third. Control semen ranged from 20 to 40 x106 sperm/dose, sorted 5° C or 18° C semen ranged from 3 to 5x103 sperm/dose, and frozen, sorted treatments ranged from 1 to 3 x 106 sperm/dose. Pregnancy rates for sexed semen in yearling heifers were 40 to 80% of those associated with conventional frozen semen controls in the first two years and as good or better numerically in 1999 as frozen, unsorted semen, but with only 1 % to 15% as many sperm per dose. Cow pregnancy rates for sexed semen were less than half to 77% of those for frozen, unsorted semen in cows, but with only 5% to 15% as many sperm per dose. Fertility of sorted sperm was higher for certain bulls: practical application of current technology may require identification of bulls whose sperm tolerate the stress of sorting and cryopreservation. particularly when low numbers of sperm are inseminated. We significantly altered the sex ratio toward 90% the desired sex of calf in primiparous and multiparous beef females. There was little embryonic death loss between 30 days and 60 days of gestation or abortion between 60 days of gestation and calving in the sexed treatments: no more losses were observed than in the controls. Calves resulting from sexed semen appear morphologically normal. In the second phase of the project, the Colorado Beef Cattle Production Model (a deterministic and stochastic simulation model) was used to examine the effects of sexed semen technology on the biological efficiency of commercial beef production when calves were sold at weaning versus when retained through harvest. Sex ratios examined included 50% with natural service, 50% with artificial insemination involving conventional, unsexed inseminate, and 60, 70, 80 and 90% with sexed semen. Production scenarios included straightbred, straightbred X terminal and rotation-terminal mating systems using either artificial insemination followed by natural service (AI+) or artificial insemination alone (AI-). The direction in which the sex ratio was skewed was determined by the type of mating. If maternal, the sex ratio was skewed toward female calves, and if terminal, toward male calves. Five products were simulated and included live weight at weaning (LWW). live weight at harvest (LW), carcass weight (CW), empty body weight at harvest (EBW) and fat free weight at harvest (FFW). Compared to natural breeding scenarios, the number of cows required to produce female replacements decreased as much as 33% as the sex ratio increased from 50 to 90%. Biological efficiency (kcal metabolizable energy per kg of beef product) for LWW increased 2.5 to 4.6% when artificial insemination was used followed by exposure to natural service cleanup. When using artificial insemination as the sole method of breeding, efficiency increased as much as 6.8%. The largest increases were observed in the straightbred mating system and at sex control of 80%. For LW, biological efficiency increased 3.3 to 4.5% and 6.7 to 7.5% when using AI+ and AI-. respectively. The largest increases were observed in the straightbred mating system at 70% sex control (AI+) and rotation-terminal mating system at 90% sex control (AI-). Similar increases in efficiency were observed for CW, EBW and FFW. Sexed semen technology added value to artificial insemination. Results suggest that sex control is beneficial at varying levels of efficacy and that sexing does not have to be perfect in order to take advantage of increases in biological efficiency. Simulated production from the Colorado Beef Cattle Production Model and budget data representing cow-calf production in Colorado were used to evaluate the economic value of sexed semen on commercial beef production at weaning. Five sex ratios (50, 60, 70, 80 and 90%), three mating systems (straightbred, straightbred by terminal, and rotation-terminal), and three methods of breeding (natural service, one period of artificial insemination followed by exposure to natural service, and artificial insemination only) were evaluated. Weaning rates included 80, 85 and 90%. The base scenario within each mating system included natural service breeding, an 85% weaning rate, and 15% replacement rate. Within each mating system, heifers and young cows were bred to produce female herd replacements while the remaining older cows were bred to produce male market offspring. As the ability to determine the sex of offspring increased from 50 to 90%, the number of cows needed to produce the required number of female herd replacements decreased 34.3 to 44.4%. allowing a larger number of cows to be transferred to the terminal breeding group to produce male market offspring. Compared to the natural breeding scenarios within each mating system, average weaning weight per cow increased, resulting in increases of gross revenue from calf sales as much as 11.8, 9.1 and 9.8% for the straightbred. straightbred by terminal and rotation-terminal mating systems, respectively. Given average market prices, an inseminate of sexed sperm targeting 90% sex ratio in favor of the preferred sex of offspring was worth $9.24 to $10.57 in a straightbred mating system using AI- and AI+, respectively. These values range from $1.01 to $3.93 and $3.30 to $5.72 for the straightbred by terminal and rota-terminal mating systems using AI+ and AI-. respectively. Besides cost and efficacy of the sexing technology, this value is dependent upon several factors, such as weaning rate (i.e. pregnancy rates and calf survival), mating system, artificial insemination program, and market conditions. Based on the assumptions of this study, the cost of sexed semen needs to be relatively close to that of unsexed semen when used in a straightbred production system; however, sexed semen appears to be economically infeasible in those systems applying crossbreeding. Furthermore, artificial insemination with conventional, unsorted semen did not appear economically feasible under the simulated conditions of this study: however, sexing added value to artificial insemination.