Should oilseed supplements be avoided in late-gestation dairy cattle diets?

Oilseed supplementation of dairy cattle diets may have negative effects during the late-gestational period.

Canadian researchers are tracking nutritional approaches or ways that dairy cow feed or diet can be used to support or improve fertility, said Divakar Ambrose, lead researcher and professor in the department of agricultural, food and nutritional science at the University of Alberta.

Nutrition for cows is of interest because poor fertility rates have been a concern for the dairy industry worldwide, he said.

“I have had a long-standing interest in studying the effects of dietary polyunsaturated fatty acids on reproductive function in dairy cattle,” ​Ambrose told FeedNavigator. ​

A study led by him, and published in the Journal of Dairy Science​, examined the impact of the inclusion of the oilseeds, canola and sunflower seeds, in the diets of pregnant dairy cattle to see what influence the diet ingredients would have on dry matter intake (DMI), plasma metabolite amounts, milk production and composition along with calf birth weight, postpartum health disorders, reproductive performance and ovarian function.

The findings indicated supplemental oilseeds at high levels may not be good additions to dairy cow feed during late-gestation. 

Prepartum oilseed supplementation (6.2 to 7.4% ether extract, % of dietary dry matter) decreased DMI during the entire experimental period (pre- and postpartum), decreased milk yield during early lactation in multiparous cows, and increased calf birth weight with no significant improvement in ovarian function and reproductive performance, wrote the team. 

“If included, [oilseeds] must be considerably lower than the level (8% DM) [dry matter] we fed in this study,” ​said Ambrose.

Canola was one of the ingredients tested because it is a common ingredient in dairy diets.

There have been inconsistent results from use of supplemental fats in previous studies, they said. And, while fat supplementation postpartum is common, less is done with it prepartum.

The study ​

In the experiment, a group of 130 pregnant Holstein cows was given one of three diets for about 35 days pre-calving, afterward all cows were given the same lactation diet, said researchers. The diets included a control and that feed with either 8% of dry matter of oleic acid or linoleic acid.

The cattle had different parity levels, meaning they had given birth a different number of times, they said.

Blood samples were taken after two weeks on the experimental diets, and at weeks 1, 2, 3, 4, and 5 post-calving to check for amounts of fatty acids, glucose and β-hydroxybutyrate (BHB), they said. And, ovarian ultrasonography was done twice a week to check for the appearance of dominant and preovulatory-size follicles and ovulation.

Uterine inflammation levels were determined at day 25 post-birth, they said. Milk production was recorded every time and feed intake was noted daily.

Results ​

Prepartum diet supplementation with the oilseeds increased postpartum DMI in primiparous cows, especially when sunflower seeds were given, wrote the researchers. But it did not alter prepartum DMI or milk yield.

But, in multiparous cows, the oilseed supplements reduced both prepartum and postpartum DMI and milk yield for the first two weeks, they noted. “Regardless of parity, prepartum feeding of canola reduced postpartum DMI compared with those fed sunflower,”​ they added.

Average fatty acid amounts were larger two weeks after the start of the feeding trial for cows getting the oilseed additives, but plasma BHB and glucose were not altered. Those cows also had longer gestation lengths and higher birth weights, especially for female calves.

Cows getting the oilseeds also had more reproductive disorders by 42% to 23%, wrote the researchers. Cows getting the sunflower seed had more occurrences of dystocia, or needing help at calving, at 35% to 18% and health disorders 52% to 32% than those getting the canola supplement.

“As calves born of cows fed oilseeds were heavier, cows would have experienced more difficulty at calving simply because of larger calves,” ​said Ambrose. “Cows experiencing difficult calving are prone for reproductive and health disorders postpartum.”  ​

The oilseed diet did not alter uterine inflammation or the time between calving and establishment of the first dominant follicle, preovulatory-size follicle or ovulation, said researchers.

What’s next? ​

The results in the study did include a few surprises, said Ambrose. These included that female calves had a heavier birth weight when the cows had a diet supplemented with the oilseeds, especially sunflower seed.

The group is uncertain what caused that effect, he said. “Although our findings need further confirmation, if the differential weight gain in female calves is repeatable in future studies, one could speculate that it may have something to do with female sex hormones regulating fatty acid metabolism,”​ he added. 

The team will also examine the use of certain long-chain fatty acids in dairy cattle diets, said Ambrose.

“We are currently investigating the effects of diets enriched in specific long chain fatty acids on early embryonic development including embryonic gene expression in pre-implantation stage embryos in dairy cows,”​ he said. “We are also studying distribution of fatty acids in the reproductive tissues of dairy cows.”​