Abstract
The objective of this study was to assess differences in reproductive performance of natural service and artificial insemination (AI) sired beef females based on pregnancy outcomes, age at first calving, and calving interval. Data were sourced from 8,938 cows sired by AI bulls and 3,320 cows sired by natural service bulls between 2010 and 2017. All cows were in a commercial Angus herd with 17 management units located throughout Virginia and represented spring and fall calving seasons. All calves were born to dams managed with estrus synchronization. Pregnancy was analyzed with generalized linear mixed models and other reproductive measures with linear mixed models in R. Six models were evaluated with the dependent variables of pregnancy status at the first diagnosis, pregnancy status at the second diagnosis, pregnancy type (AI or natural service) at the first diagnosis, pregnancy type at the second diagnosis, calving interval, and age at first calving. Independent variables differed by model but included sire type of the female (AI or natural service), prebreeding measures of age, weight, and body condition score, postpartum interval, sex of the calf nursing the cow, and management group. No differences were observed between AI- and natural service-sired females based on pregnancy status at first and second pregnancy diagnosis (P > 0.05). Sire type was only found to be significant for age at first calving (P < 0.05) with AI-sired females being 26.6 ± 1.6 d older at their first calving, which was expected because AI-sired females were born early in the calving season making them older at breeding. Surprisingly, age and body condition score were not significant predictors of pregnancy (P > 0.05). Body weight at breeding was not significant for pregnancy (P > 0.05) but was significant for age at first calving (P < 0.05). These data suggested that lighter heifers calved earlier which contradicts our original hypothesis. Overall, commercial Angus females sired by AI or natural service bulls had similar reproductive performance. Factors that were commonly associated with reproductive success were not significant in this commercial Angus herd managed with estrus synchronization. Given the size of these data, the importance of body condition, age, and weight should be reassessed in modern genetics and management practices.
Highlights
Artificial insemination (AI) as a technology has several major benefits
The AI-sired heifer calves were at least 21 d older than natural service-sired heifer calves if all the cows responded to the estrus synchronization protocol
AI-sired heifers were older at first breeding and first calving because the heifers were initially born at the beginning of the calving season and were older than their natural service-sired contemporaries
Summary
One major advantage is the ability to use semen from genetically superior bulls, enabling producers to make more precise mating decisions by mating each cow to a specific bull Another major advantage to using AI is the ability to reduce the number of bulls that are being kept on the farm making it safer for workers (Brackett et al, 1981) and reducing bull maintenance costs, potentially increasing profitability. Based on these advantages, improved adoption of AI would be beneficial for the beef industry. Other top reasons included inadequate conception percentages, lack of facilities, cost, and the complexity of the technology (Whittier, 2010)
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