Struggling with Seasonal Infertility? Prepare Your Gilts Now 

When it comes to running a sow farm, the key to success is leveraging all possible tools to meet production targets – including the gilt pool. Dr. James Lehman, DVM, technical services veterinarian with Merck Animal Health, says nearly a fourth of all litters farrowed within commercial herds come from gilt litters, resulting in a significant contribution to animal flow. 

As you prepare gilts for the breeding herd, Lehman suggests three ways to maximize potential and longevity. 

1. Manage weight and age at first heat. 
If you want to get your gilts off to the right start and set them up for long-term productivity, pay close attention to age and weight. Gilts that are too heavy at breeding are at risk for decreased longevity in the herd. Check with your genetics supplier for specific recommendations, but the following weight and age targets are applicable to most modern commercial females:

•    At final selection, gilts should be in the 225-lb. to 275-lb. range and at about 22 to 26 weeks of age. Most lines can respond to boar exposure to stimulate heat at this time. 
•    Breed on the second or third heat cycle when the gilt is 32 to 34 weeks of age and weighs between 300 lb. and 325 lb. 
•    Following these age and weight targets should result in most gilts farrowing at a weight of about 400 lb. This weight is optimal for lactation potential, decreased lifetime feed maintenance needs and overall longevity compared to gilts that are larger (450 lb and heavier) at the time of first farrowing.

“Breeding at the optimal age and weight is sometimes easier said than done, especially during seasonal infertility months when challenges include increased age at first heat and complete failure to show heat in some gilts,” Lehman says. “Farm staff must be watching more closely during these times so heat cycles are not missed.” 

Watch your gilt’s weight closely. When on ad lib feed, gilts may gain up to 20 lb. or more weekly, so delays in cycling or missed heat detection often result in gilts that are overweight at mating time. Although most farms do not weigh gilts with scales, Lehman suggests flank-to-flank measurements or girth tapes can be used to accurately estimate weights.

2. Provide the right kind of boar power.
Train your staff to heat check and make sure they understand the importance of the boar. If you are struggling to meet gilt breeding targets, review heat-no-service data frequently so you can be aware of gilt cycling problems before things get out of hand, Lehman advises. 

Be sure you have adequate boar power of the correct size and maturity. Mature boars stimulate heat better, and a boar with a strong libido will advance gilts into puberty more quickly. 

Plan to have three to five heat check boars per 1,000 females, regularly bringing new boars into your program to maintain an annual replacement rate of 40% to 60%. Many herds use Meishan crossbred boars to heat check. For operations breeding heat check boars internally, Lehman suggests ordering enough Meishan semen to farrow one or two sows per quarter to provide adequate boar power. On the other hand, if you are purchasing boars, standing orders can prevent emergency ordering. Purchased boars typically require several weeks or months to mature after arrival, he adds.  

3. Be ready to increase the gilt pool before next summer.
Consider increasing your gilt pool size now if your operation struggles with seasonal infertility. Lehman suggests renovating pens to accommodate additional gilts during the summer months. 

“Simply adding more gilts to the same pen space may actually cause additional problems,” he says. “Gilts need adequate space, ideally 12 to 15 sq. ft. per head. Overcrowding will make heat stimulation and detection more difficult. Give your genetic supplier plenty of notice of your gilt needs so they can ensure supply.”

Educate your staff on the difference between heat checking gilts versus sows, too. 

Heat detection is very labor-intensive and time-consuming, so most operations do not check heat more than once per day. Thoroughness and quality of heat detection are critical, says Todd See, department head and professor of animal science at North Carolina State University. 

“It is important to remember that each female is an individual and will show slightly different signs of estrus,” See adds. “Systematic and consistent heat checks enable one to become familiar with the normal situation of all females and when they are in estrus.”

Gilts often need more time and attention to stimulate their first heat. Lehman says extra patience is required in the gilt developer compared to heat checking weaned sows, especially in the hot months.  

Hot months also mean summer vacation for many, adding one more challenge for operations. Make sure properly trained team members are available to heat check and care for the gilt pool at all times, despite vacation plans.

Lehman says another option is to synchronize gilts with altrenogest to help effectively manage gilt breeding. It works very well, but only on gilts that have had at least one estrous cycle. It is not a substitute for heat stimulation and detection.

The gilt pool plays a critical role in your breeding herd, but it takes proper planning and consideration to help them reach their full potential. 

“Reach out for help if your gilts are not cycling as expected,” Lehman says. “Do not hesitate to contact your vet, nutritionist or other trusted expert to determine what interventions are needed to achieve maximum breeding herd success.”