Crossbreeding is not an immediate cure-all. The results will be disappointing with poor quality parent stock or with a breed or breeds that are not adapted to the environment. For a successful crossbreeding program, use breeds that contribute the highest combination to the economically important traits. For example, if a producer wants to market lambs, then ewes from breeds that excel in the following characteristics should be selected:

• Reproductive efficiency.
• Desired time and length of breeding season.
• Conception and lambing rate.
• Milk production.
• Maternal instincts.

Crossbred ewes with these characteristics could then be mated to rams of another breed to produce market lambs. Traits to look for in the ram breeds are:

• High fertility.
• Growthiness.
• Carcass quality.
• Sexual aggressiveness.

A crossbreeding program such as this would be most successful on farms where feed supplies are usually controllable and sheep are a primary source of farm income. The fine-wool breeds should be a primary source in the development of any ewe breed intended for a crossbreeding program. These breeds are particularly well adapted to New Mexico rangelands, produce the highest quality wool, are produced within the state, and have the ability to breed out of season.

If the objective is to accelerate market lamb production, it might be practical to introduce a newer breed such as the Finnish Landrace. If out-of-season breeding is not desired, the medium-wool, white-faced breeds could prove satisfactory. However, to produce market lambs, breed ewes to rams noted for their growthiness and carcass desirability. Suffolk and Hampshire generally have an advantage in desirable characteristics.

How to Select for Increased Fertility

• Identify lambs that were born as twins or triplets and select replacement lambs from this group. Twin lambs from young ewes have a greater potential for twinning than do twins from older ewes.
• If additional replacements are required, select single ewe lambs from young ewes.
• Select rams that were twins or from ewes that had high twinning records. Scrotal circumference should be 28 cm for 12-month-old rams and 32 cm for mature rams.
• Ewe lambs that exhibit estrus are typically more fertile and have a greater lifetime production of lambs than ewe lambs that do not reach puberty the first year. Selecting early maturing ewe lambs also emphasizes early season lambing, which might be advantageous in some management systems.