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The Dairy Cattle Reproduction Council is pleased to continue the DCRC newsletter. This newsletter will give highlights of current hot topics and research in dairy cattle reproduction, as well as recaps of presentations from the 2007 DCRC meeting. |
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Pregnancies are extremely important to dairy profitability, but how much is a pregnancy really worth to your operation? Financially, improving pregnancy rates can have a major impact on profits, as well as replacement animals and reproductive costs. Click here to learn more about how valuable pregnancy can be to your operation. ET Shown to Improve Conception Rate More Than Artificial Insemination A study recently performed in Brazil evaluated factors that may influence conception rate (CR) after artificial insemination (A.I.) or embryo transfer (ET). The study results were published in the Journal of Dairy Science. Cows producing approximately 57 to 88 pounds of milk per day received one shot of PGF2α and were randomly assigned to one of two groups: (1) A.I. or (2) ET. The cows were pregnancy checked at 28 days and 42 days after estrus. Ovulation, conception and embryonic loss were analyzed to evaluate the effects of days in milk, milk yield, body weight and concentration of progesterone in the blood on CR. Researchers analyzed four groups of cows: (1) cows in estrus, (2) cows with a corpus luteum on day seven, (3) ovulating cows seven days after estrus and (4) cows experiencing embryonic loss. The results showed that the transfer of fresh embryos increased the probability of conception because it avoided the negative effects of milk production and low progesterone on the early embryo. ET was shown to be superior to A.I., especially in high-producing cows. High body temperature had a negative effect on CR and the embryo’s survivability. To read the entire study, click here. Reproduction Traits Have Direct Impact on Functional Longevity in Canadian Dairy Cattle Canadian researchers recently completed a study to assess the relationship between reproduction traits and functional longevity. The reproductive traits included calving traits and female fertility traits. The data set consisted of 1,803,517 Holstein, Ayrshire and Jersey cow records, and included the effects of stage of lactation, season of production, annual change in herd size and milk testing system. Age at first calving, milk yield, fat and protein were also calculated. Associations between reproduction traits and longevity were significant and observed in all breeds. The risk of culling increased in cows that required hard pull, had small calves, or dead calves. Cows were also at greater risk of being culled if they required an increased number of services per conception or had a longer interval between first service and conception. In addition, cows with more than 90 days between calving and first service and cows with a greater number of days open were also at an increased risk. To read the complete Journal of Dairy Science study, click here. Time of the Second GnRH Injection and A.I. during Ovsynch® Affects Conception Rate
In the study, 927 lactating dairy cows were blocked by pen and pens rotated though treatments. All cows received GnRH and, 7 days later, a shot of PGF2a. Each was then placed in one of three treatment groups: Cosynch-48 (GnRH + timed A.I. 48 h after PGF2α), Ovsynch®-56 (GnRH 56 h after PGF2α + timed A.I. 72 h after PGF2α) or Cosynch-72 (GnRH + timed A.I. 72 h after PGF2α). Overall CR was similar in the Cosynch-48 and Cosnych-72 groups as seen in the table. However, the Ovsynch-56 group had a greater CR than both of the Cosynch groups. The study also found that presynchronized first-service animals had greater CR than cows in later services in the Cosynch-48 and Ovsynch-56 groups, but not in the Cosynch-72 treatment. Likewise, first lactation cows in the Cosynch-48 and Ovsynch-56 groups experienced higher CR than second lactation or greater cows. CR was similar regardless of parity in the Cosynch-72 group. Researchers determined there was a clear advantage to administering GnRH at 56 hours, 16 hours before a 72-hour A.I., most likely due to a more optimal time of A.I. before ovulation. To learn more, click here. Environment Influences on Conception Rate A recent study conducted at the University of Georgia investigated how milk production, service month and days in milk (DIM) affected conception rate (CR). Recent A.I. and Herd Improvement records were used in the study. 298,015 service records for 160,879 cows in New York and 23,366 records for 12,184 cows in Georgia were used in the study’s data set. From the records, researchers concluded the following about each relationship:
We've put together a roundtable featuring veterinarians and dairy producers who discuss the variety of reproductive technologies used on the farm and how each can be implemented in different situations. To meet the roundtable participants and learn about their recommendations, click here.
A net present value (NPV) model of a dairy cow, developed by Dr. David Galligan of the School of Veterinary Medicine at the University of Pennsylvania, looks at the impact various parameters have on the economic value of a cow per year. Parameters having the greatest effect on profit/cow/year:
Reversing genetic mismatch Rapid changes in genetic potential, average herd size and indoor housing have created a mismatch between the genotype of high-producing dairy cows and herd environment. According to Chad Dechow of Pennsylvania State University, this mismatch has compromised cow fertility. There are, however, tools available to reverse these negative trends. Selection for higher daughter pregnancy rate will directly improve fertility whereas selection for higher productive life (thereby less focus on dairy form) will indirectly increase fertility. Selection indexes, such as lifetime net merit or total performance, incorporate these traits along with other economically important traits to provide a balance between fertility and production. Dechow also notes producers should approach fertility improvement from genetic selection with a sense of urgency to respond to potential consumer pressure in regards to reproductive hormone use. Lameness affects reproduction The National Animal Health Monitoring System Dairy 1996 Study reported lameness was the reason for culling 15 percent of dairy cows. Study results have also shown lameness to be a predisposing factor for delayed ovarian cyclicity and a prolonged calving-to-conception interval. Dr. Jorge Hernandez says it’s hypothesized that lameness during lactation has an effect on feed intake, energy status and, subsequently, ovarian activity. The detrimental effect of lameness on time-to-conception becomes greater as lameness severity increases. In a Pennsylvania study, lame cows had a 28-day longer calving-to-conception interval when compared to nonlame cows. Additionally, a University of Florida study identified claw lesions as the main cause of lameness and impaired reproductive performance. Screening and hoof trimming procedures can help reduce incidence of lameness during late lactation. Producers are encouraged to use locomotion scoring for early detection and management of lameness. To access the full papers from the 2007 DCRC Convention, click here.
Several studies have attempted, through various methods, to investigate in vivo uterine activity. The purpose of this more recent study was to compare the effects of luteolytic doses of D-cloprostenol, natural prostaglandin F2α, DL-cloprostenol, and a placebo on intrauterine pressure and motility during diestrus. The study consisted of eight lactating Red-Holstein and Simmental crossbred cows housed on a conventional farm in Switzerland. The study began one to two weeks after the onset of estrus in each cow. Cows received intramuscular injections of each of four treatments: 1) 25mg dinoprost, 2) 0.5mg DL-cloprostenol, 3) 0.15mg D-cloprostenol and 4) 5.0mL placebo, with a natural heat occurring between each session. The order of each cow’s treatments was determined by two 4X4 Latin-square patterns. Intrauterine pressure was monitored in a uterine horn by a catheter equipped with pressure sensors for thirty minutes prior to treatment. Pressure was then monitored in fifteen minute increments for another two hours after the drug was administered. Blood plasma levels were measured before and after each trial to detect luteolytic phase and to verify estrus. Researchers concluded that natural prostaglandin F2α had the most effect on uterine motility and pressure, indicating it would have the greatest effect on inducing luteolysis, thus activating follicle development. This result was most likely due to more favorable attraction of the treatment to uterine receptors. To view the complete study from Theriogenology, click here. (This case study was brought to you by Schering-Plough Animal Health) | |||||||||||||||||
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