The ram plays a critical role in flock fertility, genetic progress, and breeding efficiency. Indeed, the reproductive and genetic contributions of a single ram are disproportionately high due to the low joining ratios used in most breeding systems, and the subsequently large numbers of lambs sired by each male. This post reviews the importance of the ram in sheep breeding and how veterinarians and producers can optimise ram management – from understanding male reproductive physiology, to ensuring breeding soundness, managing joining ratios and selecting rams to meet breeding and production objectives for their enterprise.
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Understanding basic male reproductive physiology is important for managing ram fertility. The testes of the ram produce sperm continuously after puberty. It takes approximately 7 weeks for a complete cycle of sperm production (spermatogenesis) to be completed in the ram, plus an additional 2 weeks of maturation in the epididymis (1). This long lead time means any stress or illness can affect sperm quality for months after the event, underscoring the need to prepare rams well in advance of breeding.
Spermatogenesis is governed by the reproductive hormone axis. The production of GnRH by the hypothalamus stimulates the pituitary gland to release gonadotropins (LH and FSH) that in turn stimulate testosterone production by the Leydig cells of the testes. Testosterone is essential for sperm production and epididymal maturation. Unlike ewes, which have obvious oestrous cycles, rams maintain sperm production all year. However, some seasonal variation in sperm production does exist, with sperm numbers, testis size and testosterone levels all affected (2). This seasonality is driven by changing daylength (photoperiod) via the neuroendocrine transducer melatonin (1).
Environmental factors also influence ram fertility. Temperature is critical, since the testes must stay a few degrees cooler than body temperature for normal sperm production. Heat stress is a common cause of poor fertility, and it may take several weeks or even months for sperm quality to recover. Adequate nutrition is equally important. For example, improving a ram’s nutrition 7–10 weeks before breeding (e.g. with energy-rich supplements like lupins) can significantly increase testis size and sperm output (3). In practice, rams should enter the breeding season in good body condition (score 3; not over fat) and free of nutritional deficiencies.
A Breeding Soundness Evaluation (BSE) should be performed 2–3 months before joining to ensure each ram is fit for mating (1). A standard BSE involves a thorough physical exam and reproductive assessment, often described as the "4T’s": teeth, toes, testes, and tossle (penis).
A semen evaluation may also be performed, particularly on high-value rams or those destined for single sire mating. Semen is assessed for motility, morphology, and concentration. Rams with ejaculates that consistently contain <30% motile sperm, <70% normal sperm and/or <2 billion sperm/ml should be excluded from breeding as should those males which fail the 4Ts (1, 3).
Studies show that 1% is often sufficient to maintain good flock fertility (1). Individual rams with good breeding soundness can impregnate 160–300 ewes within three weeks. However, below 1%, the risk of ewes not being served during early oestrus increases, especially in the first 17-day oestrous cycle.
Several factors warrant higher joining ratios, including poor nutrition, out-of-season breeding, joining maidens, small or widely dispersed flocks, extreme terrain or temperatures, and syndicates with too many very young or old rams. In such cases, an extra ram per 100 ewes may be needed. Despite these nuances, most producers err on the safe side with a 2% joining ratio (1).
A 5-week joining period, or roughly 3 oestrous cycles, should be employed.
Genetic gain in a flock is often primarily made through the male line. Rams contribute 50% of the genes to all their offspring, but in most systems, far fewer rams than ewes are used. This makes selection pressure on rams far more potent than on ewes.
Traits like growth rate, muscling, wool quality, and even worm resistance are all heritable and can be improved in a flock through careful ram selection using Estimated Breeding Values or other genetic tools.
Melatonin implants, widely used to induce cyclicity in ewes during the non-breeding season, are now also gaining traction as a means to enhance ram fertility. Recent Australian research (2) has demonstrated that exogenous melatonin can significantly increase testicular size and sperm output in rams during the non-breeding season. Treated rams also had elevated blood testosterone levels and greater sperm numbers per ejaculate, reflecting improved testicular function. These effects were apparent from three weeks post-implantation and persisted for several weeks. Spermatogenic output was normal in treated rams the following breeding season. These results suggest that melatonin supplementation can both advance the ram breeding season and enhance reproductive performance, offering producers greater flexibility in managing mating programs out of season.
(1) de Graaf S.P. (2010) Reproduction. In 'International sheep and wool handbook'. (Ed. DJ Cottle). pp. 189-222. (Nottingham University Press: Nottingham)
(2) Pool, K.R., Pini, T., Rickard, J. P., & de Graaf, S.P. (2020). Exogenous melatonin advances the ram breeding season and increases testicular function. Scientific Reports, 10, 9711
(3) Abbott, K. (2018) The Practice of Sheep Veterinary Medicine. University of Adelaide Press.