Wednesday, August 14, 2019

Fertility Testing

On August 6, the lambs were evaluated for fertility traits: libido (mating desire) and semen quantity and quality. The testing was done by Dr. Stephan Wildeus and Dr. Dahlia O'Brien from Virginia State University. Youth participating in the 4-H Research Academy assisted with data collection.

Each lamb was put in a pen with two mature ewes for 5 minutes. The ewes had previously been treated with CIDRs so that they would be in estrus (heat) at the time of testing. Two pens (8 ft. x 8 ft). were set up side-by-side. Reproductive behaviors were observed and recorded. The time to first service was measured in seconds.

Evaluating libido in male lambs

Intact males (rams) and short-scrotum rams exhibited similar mating behavior (libido), with no statistical differences. The only observed mating behavior in the wethers was sniffing, but it was less than ram and SC lambs.

  Sex No. Sniff Butt Kick Flehmen Mount Service Time
(sec)
  Ram 21 3.54a 0.10a 1.59a 0.47a 1.50a 1.30a 217
  Short scrotum 18 3.46a 0.05a 0.73ab 0.42a 1.24a 0.45ab 244
  Wether 25 1.33b 0a 0b 0b 0b 0b na
  Probability
0.0001 n.s. 0.0039 0.0039 0.0410 0.0060 n.s.
Data with different subscripts are statistically different. n.s. = non-significant

Observed behavior was similar between pens (ewes) and indicated that teaser ewes in both pens displayed estrus adequately, with the only statistical difference being for kicks.

  Pen No. Sniff Butt Kick Flehmen Mount Service Time
(sec)
  A 32 2.98 0.06 1.21 0.36 1.15 0.64 214
  B 32 2.58 0.04 0.33 0.23 0.67 0.53 247
Probability 0.389 n.s. 0.0252 n.s. n.s. n.s. n.s.
n.s. = non-significant

Using an estrus ewe, semen was collected from lambs with an artificial vagina (AV). Samples were obtained from seven ram lambs and seven short-scrotum lambs. The semen was evaluated on-site.

Ejaculates from SC (L) and ram lamb (R).
Intact and short-scrotum rams produced similar ejaculate volumes; there was no statistical difference. The semen from rams had 45.0% mobility, whereas the semen from the short scrotum rams had only 5.7% mobility. The semen from the rams had a greater concentration of sperm cells: 1.52 billion per ml vs. only 0.049 billion per ml for the short-scrotum rams.

  Sex No. Volume, ml Mobility, % Concentration, b/ml
  Ram 6 0.56a 45.0a 1.52a
  Short scrotum 6 0.49a 5.7b 0.049b
  Probability
0.5566 0.0089 0.0152
Data with different subscripts are statistically different. n.s. = non-significant

Unlike last year, some sperm cells were observed in the ejaculates of short-scrotum rams. Some sperm mobility was also detected. A possible reason is that the short-scrotum procedure was done when the lambs were older (unlike last year), as some of the short-scrotum rams had noticeable scrotums.

Sperm mobility and concentration was less for the intact rams, as compared to last year. This may be because they weren't as far along in pubertal development. Age will be added to the statistical model.

The preliminary conclusion is that the short-scrotum rams would not work for breeding. However, there is no guarantee that they could not impregnate females.This differs from last year, when SC were deemed infertile, based on semen evaluation.

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