WHEN it comes to Holstein dairy cows and how much milk they produce for their offspring, Kansas State University and Harvard University researchers have determined that daughters are preferred.
A study of 2.39 million lactation records from 1.49 million dairy cows showed that cows produce significantly more milk for daughters than for sons across lactation, said Barry Bradford, an associate professor in Kansas State's department of animal sciences and industry.
He collaborated on the study with Katie Hinde in Harvard's department of human evolutionary biology, graduate student Abigail Carpenter at Kansas State and John Clay with Dairy Records Management Systems in Raleigh, N.C.
"Our results provide the first direct evidence that the sex of a gestating fetus can influence milk production," Bradford said. "One possible explanation is that a daughter is able to let her mom know, in advance, that she expects to receive more milk than her brothers."
In addition, the researchers found that the sex of the fetus a cow is carrying can enhance or diminish the production of milk during an established lactation and that the sex of the fetus gestated in the first pregnancy has persistent consequences for milk production on the second lactation.
Results of the study are available in PLOS One.
The study also could have implications for humans, Hinde said.
"Among the surprises in this study was the fact that the bias was in favor of daughters rather than sons, as some evolutionary hypotheses have predicted. Daughters seemed to have the most dramatic effect on the initial development of the mammary gland, because the bias against sons was greatest in the first lactation," Bradford said.
The team also found that the percentages of fat and protein in milk did not differ among cows that gestated a son or daughter, so the quality of milk was the same. However, because the quantity was greater after gestating a daughter, the total amounts of milk fat and protein after gestating a daughter were higher than after gestating a son.
Standardized husbandry in the dairy industry, combined with systematic milking procedures, detailed recordkeeping and large sample sizes, made the dairy cow a powerful model for the exploration of milk synthesis, the researchers explained.
The study was derived from all of the lactation records from 1995 to 1999 in a database managed by Dairy Records Management Systems.
How does the fetus influence milk synthesis? It's likely that hormones from the fetus and placenta differ between fetal sons and daughters. Those hormones may subsequently enter the maternal bloodstream and affect milk-producing cells in the mammary gland, the researchers said.
"After finding the programming effect of fetal sex on subsequent lactations, our team discussed the possibility that daughters were releasing hormones into the maternal circulation that could directly influence the mammary gland," Bradford said. "It occurred to us that if this was true, becoming pregnant with a daughter might influence milk production even in an ongoing lactation. I was floored when we tested that effect and found it to be significant as well."
Cows that had two daughters back to back produced about 445 kg (about 980 lb.) more milk across the first two lactations than cows that had back-to-back sons, he said.
Artificial insemination is standard practice in the dairy industry, and producers have the option of buying sex-selected semen.
"According to our rough calculations, taking into account the wholesale value of milk, the number of two-year-old heifers added to U.S. dairy herds annually, the production advantage across the first two lactations of conceiving a daughter on the first pregnancy and the increased probability of conceiving a daughter from sex-selected semen suggests a gross value in the neighborhood of $200 million in milk production across the first two lactations alone," the team reported.
A recent study conducted at the University of British Columbia explored the conditions in which indoor-housed Holstein dairy cows would seek shelter during calving, if at all.
This research was originally published in the Journal of Animal Science.
While it has been suggested that a better understanding of the maternal behavior of dairy cows may help producers improve care, there has been little research to determine whether, and under what conditions, indoor-housed cows will hide during calving when shelter is available.
Study researchers, led by Dr. Marina von Keyserlingk, aimed to determine whether indoor-housed dairy cows would seek shelter to calve, if given the chance, and whether such behavior is influenced by the time of day or the presence of other cows in the pen.
For this study, Holstein cows were paired by expected calving date, moved into maternity pens before their expected calving and monitored with video cameras that recorded continuously. The pens contained an open area with no cover and a sheltered area that was covered on all sides, except for the ceiling and an opening where cows could enter and leave freely. When one cow in a pair calved, she was removed from the pen, leaving the second cow alone in the pen.
Results showed that single-housed cows were more likely to calve in the shelter, but only when calving during the day, and that pair-housed cows were more likely to calve in the open area, regardless of the time of day, the researchers said.
Results also showed that for individually housed cows, the use of the shelter increased approximately eight hours before calving, and for pair-housed cows, separation from their partner also began around eight hours before calving. These times may coincide with the onset of the first stage of labor, the researchers pointed out.
Animal welfare scientists at the Koret School of Veterinary Medicine of the Hebrew University of Jerusalem in Israel and the University of Bristol School of Veterinary Sciences in the U.K. have been investigating the potential of a novel method for assessing the welfare of dairy cows.
The research could provide early indications of health and welfare problems and help with more timely and effective interventions.
In a paper published in the October 2013 Journal of Dairy Science, Roi Mandel and the research team at the Koret school described how they have investigated the cows' changing patterns of use of automated scratching brushes — devices that are increasingly provided in dairy farms for the animals' benefit — as behavioral indicators of stress and discomfort, correlating usage with the cows' own feeling of well-being.
The hypothesis, which appears to be supported by the results of the research so far, is that if a cow is beginning to feel unwell, this will manifest in reduced brush use — data that can be automatically collected by the brushing device and suggest further investigation. The hope is that serious conditions such as mastitis could be detected earlier, leading to more effective intervention, the researchers said.
Further research will be undertaken to assess the sensitivity of the method and the correlations between brush usage and specific conditions.
Mandel's research, supervised by Dr. Eyal Klement of the Koret school and Dr. Becky Whay and professor Christine Nicol from the University of Bristol animal welfare and behavior research group, is supported by the Universities Federation for Animal Welfare, a U.K.-based charity that has a special fund to help the development of animal welfare science in Israel.
"We are delighted that this research project could lead to significant advances in dairy cow welfare not only in Israel but around the world," federation chief executive and scientific director Dr. James Kirkwood said.