Reproductive Management Strategies for Dairy and Beef Cows

Dear Colleagues,

The adoption of reproductive technologies and adequate reproductive management practices has been vital in the acquisition of superior genetics, enabling  rapid genetic improvements in herds in recent decades. The dairy industry has greatly benefitted from this, with reports of only 10.7% of dairy operations adopting a natural service by 2014. This rapid adoption of reproductive technologies has enhanced the efficiency of milk production, with the United States dairy industry producing 84.3 billion kg of milk with an inventory of 9.2 million cows in the year 2007; this is in contrast to 53 billion kg of milk and an inventory of 25.6 million cows in 1944. Nevertheless, the genetic selection of dairy animals has been focused on high achieving yields of milk, resulting in the decreased fertility of lactating cows over the years; indeed, the peak of infertility was observed around the year 2000. An adequate understanding of high-producing lactating cows has enabled the development of novel reproductive management practices that have resulted in the increased fertility of dairy females.

In the beef industry, several reproductive technologies and management practices have been developed in recent decades and contributed to the promotion of cow–calf operations; these include, but are not limited to, an enhancement in the accessibility of superior genetics, the induction of cyclicity in anestrous females, and early calving. Nevertheless, the adoption of reproductive technologies by beef producers has been slow, and the development of proper reproductive management practices aimed at improving the reproductive efficiency of beef herds is required in order to enhance the adoptability of reproductive technologies by the beef industry. We are pleased to invite you to submit your work related to the area of reproductive management strategies for beef and dairy cows.

This Special Issue aims to highlight and provide insights into current research addressing the development of novel reproductive management strategies that could enhance the reproductive efficiency of beef and dairy cows. Research areas may include (but are not limited to) the following:

• The development of novel estrus synchronization programs;
• The development of novel vaccine programs that result in improved reproductive efficiency;
• Nutritional strategies that result in improved reproductive efficiency;
• Management strategies that improve reproductive efficiency.

Dr. Nicholas Wege Dias
Guest Editor

Manuscript Submission Information

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• bovine reproduction
• reproductive technology and management
• theriogenology
• endocri-nology

Title: Estrus Expression Preceding Fixed-Time Artificial Insemination Is Positively Associated with Fertility of Heifers and Lactating Dairy Cows
Authors: Leticia P. Sanglard; Jeffrey S. Stevenson; Milton Schultz; Victor Gomez-Leon
Affiliation: Department of Animal Sciences and Industry, Kansas State University
Abstract: GnRH-based protocols for fixed-time artificial insemination (FTAI) in dairy cattle may limit the incidence of estrus expression; however, the potential benefits of estrus expression during a FTAI program in dairy cattle are controversial. The current observational study aimed to assess the association expression, intensity, duration, and timing of estrus preceding FTAI with pregnancy per artificial insemination (P/AI) and calving risk of heifers and lactating Holstein cows submitted to GnRH-based FTAI protocols at first service. Only first services resulting from FTAI protocols (PG3G for cows at 75 ± 3 DIM and CIDR-synch for heifers at 400 to 430 d of age) were used. Moreover, only estrus events during 48 h before FTAI were used to categorize animals in the estrus group. Animals that expressed estrus from D –8 to –2 and from D 1 to 5 in relation to the FTAI (D 0) were removed. Data analyzed included 1,154 breeding records, 359 estrus measured by an automated activity monitor, pregnancy diagnoses, and 323 calvings from January 2021 through September 2024. Logistic regression models were used to associate P/AI and estrus expression, estrus intensity (3 to 15.9 units), estrus duration (4 to 32 h), and time from estrus to FTAI (–48 to 0 h). Parity (nulliparous, primiparous, or multiparous) was fitted as a fixed effect in the models, whereas random effects included AI sire, AI technician, and year/season of AI. Incidence of estrus expression was greater (P < 0.001) in heifers than in cows (57 vs. 33%). Our main hypothesis that estrus expression would be associated with greater P/AI and calving risk in dairy cattle regardless of their parity was supported. When estrus was not expressed, the P/AI was 53% for heifers, 49% for primiparous cows, and 41% for multiparous cows. Estrus expression was associated with 10, 10, and 16 greater (P = 0.002) percentage-points of P/AI in heifers, primiparous, and multiparous cows, respectively. In general, dairy cows and heifers had greater odds (odds ratio [95% CI] = 1.63 [1.20; 2.23]) of being pregnant at 34 ± 3 d after AI when estrus was expressed. In addition, animals expressing estrus during 0 to 18 h before FTAI (h 0) had greater odds (P = 0.05) of P/AI than animals expressing from 48 to 18 h before FTAI. Finally, animals expressing estrus tended (P = 0.06) to have a greater calving risk (least square probability of calving = 0.98 [0.91; 0.99]) than animals not expressing estrus (0.90 [0.80; 0.95]). Our results failed (P ≥ 0.58) to support the hypothesis that estrus intensity and duration measured by an automated activity monitor was associated with the fertility of dairy cattle submitted to FTAI. In conclusion, estrus expression was associated with greater P/AI and tended to be associated with greater calving risk in FTAI heifers and lactating cows.