An international team of researchers examined the use of different diet and feed intake on super-ovulatory response and embryo production in heifers in Brazil. The group published its research in the journal of Theriogenology
“The objective of this study was to evaluate the chronic effect of distinct levels of DMI [dry matter intake] on multiple ovulatory response, and the quantity and quality of embryos produced in Bos indicus heifers,” said the researchers.
The group found that despite lower body condition score, cattle getting the limited diet produced more recoverable ova and had great follicle development.
“High feed intake for more than seven weeks compromised the super-stimulatory and super-ovulatory responses of Bos indicus heifers, probably due to a lower ovarian sensitivity to FSH [follicle-stimulating hormone] associated with hyperinsulinemia,” they said.
Why feed intake and super-ovulation?
When using FSH protocols, there continues to be variation in super-ovulatory response in cattle, which limits “the profitable and efficient implementation of embryo technology” in cows, said the researchers. About 20% of cows are able to generate the majority of viable embryos after several ovulation treatments.
Nutritional management appears to have an influence on the multiple ovulatory response and embryo production, they said. However, embryo donors are often overweight and overfed from poor nutritional management which may be limiting oocyte and embryo quality.
Antral follicle count (AFC) at the start of an FSH series is considered the most important factor affecting embryo production, they said. It has a positive correlation with multiple ovulatory response and embryo yield.
“Nutritional flushing prior to multiple ovulation treatments has been related to increased number of small follicles in the ovaries, apparently through an increase in circulating insulin-like growth factor 1 (IGF1) and insulin,” said the researchers. “It has been reported that these factors increase the sensitivity of granulosa cells to FSH.”
But the amount of insulin in the blood also has been linked to reduced AFC, poor embryo quality and reduced ovulatory response, they said.
Additionally, there is discrepancy in the influence of dietary energy levels and dry matter intake (DMI) on ovulatory response, they said. Research has found both positive and negative effects from DMI on multiple ovulatory response.
High-energy diets also have been linked to compromised embryo production and altered gene expression, they said.
In the experiment, 39 Nelore heifers were kept on one of two diets for a period of nine weeks, said the researchers. Prior to the start, all heifers were given the same maintenance diet for 21 days.
One group, on the high diet, had a hay-corn silage diet at 170% or 2.6% of body weight (BW) in dry matter (DM), the other group received the low hay-corn silage diet at 70% or 1.1% of BW in dry matter.
Body weight was measured weekly, said the researchers.
On week seven, heifers started being given eight decreasing does of follicle-stimulating hormone (FSH) and inseminated, said the researchers. After seven days, heifers had their uteri flushed, and the embryos were graded.
Blood samples were taken on day four for the FSH series and ovarian follicles at or larger than 3mm and 6mm were counted on days four and seven, respectively. On day 10, follicles 6mm or larger were considered anovulatory follicles and on day 15. the amount of corpora lutea (CL) was checked to estimate super-ovulatory response.
At the start of the FSH period, heifers getting the high diet had higher body condition scores (BCS), increased body weight and elevated serum insulin concentrations, when compared to those getting the low diet, said researchers.
“There was a tendency for a difference between diets in number of follicles ≥ 3 mm in diameter at the time of the first FSH treatment,” they said. “Moreover, 0.7 M [low diet] heifers had twice as many follicles ≥ 6 mm in diameter at the time of the last FSH treatment, more CL at embryo flushing, as well as a greater numbers of ova and embryos, and viable embryos than 1.7 M heifers.”
A negative relationship between the amount of circulating insulin and follicle super-stimulatory reaction to FSH was found in the trial, they said. But, it did not alter ovulation rate or embryo quality.
“Therefore, we conclude that high feed intake, for a long period of time, compromised the super-ovulatory response and embryo production potential of Bos indicus heifers possibly related to the elevation in circulating insulin,” they said.
Prior to running the experiment, the team had not set a preconceived hypothesis as there had been conflicting data, said the researchers. “In reality, the observed results while extremely dramatic were somewhat unexpected and unprecedented,” they added.
“Our results did not provide evidence for a direct effect of a prolonged elevation in feed intake and extremely elevated circulating insulin on fertilization rate or early embryo development, as measured by morphological embryo quality,” they said. “However, our results provide strong and dramatic support for an effect of prolonged elevations in insulin, due to high feed intake, producing reduced responsiveness of follicles to FSH stimulation.”
Title: Embryo production in heifers with low or high dry matter intake submitted to superovulation
DOI: published online before print: 10.1016/j.theriogenology.2017.01.015
Authors: M Mollo, P Monteiro Jr., R Surjus, A Martins, A Ramos, G Mourão, L Carrijo, G Lopes Jr., R Rumpf, M Wiltbank, R Sartori