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Published: Thu, May 18, 2017
World | By Tasha Manning

Late ovulators can become difficult breeders

Late ovulators can become difficult breeders

The author is a professor of animal sciences at Kansas State University, Manhattan. Reestablishing estrous cycles after calving has been studied since the 1920s. Back then, Sir John Hammond of Cambridge made some of the first recorded observations in dairy cattle. Early studies estimating normal estrous cycles were based on visual detection of estrus, palpation of the ovaries, or both.

Later, with the use of progesterone immunoassays or blood, onset of progesterone secretion by the first postpartum luteal structure or corpus luteum could be determined by scientists. With these tools, research has focused on when and how first ovulation occurs and what factors are possibly controlling (stimulating or inhibiting) the first luteal function in the dairy cow.

As we delve deeper into this topic, let's begin by defining some terms. Then, we will examine some of the recently identified factors that are associated with first postpartum estrous cycles.
Confusing terms A number of terms are used interchangeably when describing the onset of postpartum estrous cycles. Anestrus literally means lack of estrus or estrous cycles - a common occurrence during pregnancy. This term can be confused with anovulation which is lacking of regular estrous cycles each associated with ovulation.

Cholb'al Q'ij
Kk'extaj ri ub'anik, ub'anik xuquje 'ri kuk'ulula'j wi rib' ruk 'nik'aj chi b'anoj xuquje' eta'mab'al, ri kk'utuw ri maj uk'isik. You think why I am like this, why does that always happen to me? There begins the very act of deciding for the first time.

For example, the cow may be defined as anestrous but having regular ovulatory cycles when it does not display any heat signs before ovulation. Furthermore, a cow may be anovulatory (not ovulation) but displaying regular signs of heat. The former (anestrus but ovulating regularly) is very common. It indicates lack of good heat detection on the farm.

They studied 219 cows in four commercial herds and monitored ovarian activity by collecting milk samples twice weekly and measuring progesterone. Where other researchers arbitrarily chose some threshold cutoff for cows that were considered to have delayed or nondelayed first postpartum ovulation, the Japanese study determined in these herds that the threshold to define delayed ovulation was 35 days because cows ovulating after that time had reduced fertility. The table illustrates two studies by these authors summarizing some characteristics of postpartum cows as they first ovulate and summarize estrous cycles. Note that less than 50 percent of cows had resumed estrous cycles by 35 days in milk - not different from studies in the U.S. From 12 to 16 percent of cows had prolonged luteal phases after ovulation had occurred. Prolonged luteal phases were defined as periods exceeding 20 days when progesterone concentrations were elevated (& gt; 5 ng / mL) in the absence of insemination. These extended luteal periods occurred because the corpus luteum was maintained and failed to regress. Short luteal phases (3 to 7 percent) were characterized by shorter than normal luteal function after ovulation, except for the first estrous cycle which is typically shorter than 20 days in dairy cows.

Some of the risk factors include fresh cow health disorders and age. Fresh cow care, including clean calving areas, monitoring transition cows closely for subclinical signs of ketosis and milk fever, and adequate dry matter intakes, will likely reduce some of these risk factors for late ovulation. Happy A.I. Breeding!

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