Influence of dietary protein on parasite establishment and pathogenesis in Finn Dorset and Scottish Blackface lambs given a single moderate infection of Haemonchus contortus

An experiment was conducted to examine the influence of dietary protein on parasite establishment and pathogenesis of Haemonchus contortus in lambs of two breeds. Finn Dorset and Scottish Blackface. The lambs were introduced to high protein (170 g crude protein (CP) kg-1 dry matter (DM) or low protein (88 g CP kg-1 DM) diets at three months old and infected one month later with 125 larvae (kg bodyweight)-1. Blood and faecal samples were collected for analysis and bodyweights recorded weekly. The lambs were killed 20 weeks after infection. A second experiment was conducted in Blackface lambs solely to determine the influence on parasite establishment of the high and low protein diets following infection with 125 larvae kg-1. These lambs were killed five or 14 weeks after infection. Results showed that in Scottish Blackface lambs dietary protein did not significantly influence the establishment of H contortus. However, in Finn Dorset lambs dietary protein may have influenced parasite establishment since lambs on the low protein diet had a higher faecal egg output four weeks after infection and more severe clinical signs than infected lambs of the same breed on a high protein diet.     

The effect of dietary protein on the pathophysiology of acute ovine haemonchosis

An experiment was conducted to examine the effect of dietary protein on the pathophysiology iof acute haemonchosis in Finn Dorset/Dorset horn lambs.

Erythrokinetic and metabolic studies using ⁵¹Cr-red cells, ⁵⁹Fe-trasferrin and ¹²⁵I-albumine and digestive efficiency and nitrogen balance measurements wer conducted between 19 and 39 days after infection. Identical radioisotopic and nutritional studies were conducted later on pair-fed control lambs.

The results demonstrated that lambs on a law protein diet (88 g crude protein (CP) kg⁻¹ dry matter (DM)) were less able to withstand the pathyphysiological consequences of infection with 350 Haemonchus contortus larvae kg⁻¹ body weight than lambs given a high protein (170 g CP kg⁻¹ DM) diet, despite similar worm budens.

Erythrokinetic studies indicated that abomasal blood loss was similar in both groups of infected lambs, and circulating red cell volumes were reduced and plasma volumes were expanded to a similar degree in both groups. The majority of infected lambs in both dietary groups responded equally well to the gastric haemorrhage by increasing the rate of red cell production and their absorption of dietary iron was greater than in the control lambs. Albumin catabolism was increased in both groups of infected lambs, particularly in those given the low protein diet.

Within each dietary group there were no differences in the digestibilities of the various proximate fractions of the experimental diets and no differences in the urinary of faecal nitrogen losses between infected lambs and their pair-fed control. However, loss of appetive was a major feature of the disease, particularly in the lambs given the low protein diet and this feature appeared to be crucial in determining the ability of the infected sheep to withstand the pathophysiological effects of the parasite.     

Influence of dietary protein on the pathophysiology of haemonchosis in lambs given continuous infections

Mixed-sex groups of three-month-old Finn Dorset and Dorset Horn lambs were given complete diets containing either high or low protein. A trickle infection with Haemonchus contortus of 200 larvae, given three times a week, began one month later for a 17 week period. Erythrokinetic, metabolic, digestibility and balance studies were conducted with the male lambs during weeks 12 to 14 of the infection. Clinical signs of haemonchosis became evident only in the low protein diet group. The infection was characterised by severe macrocytic anaemia, hypoproteinaemia, hypoalbuminaemia, reduced survival, high egg counts and a significantly greater worm burden. In the high protein diet group many lambs developed resistance to further infection in contrast to the low protein group in which no resistance developed. Live-weight gain was not affected by infection in the high protein diet group but decreased in the lambs given the low protein diet compared with uninfected controls. However, infection did not appear adversely to affect the digestive efficiency, nitrogen retention or iron absorption in either dietary group although loss of appetite occurred in the low protein group. Examination of a sample joint from the carcases showed infection was associated with a marked reduction in muscle mass in lambs given the low protein diet relative to the control animals.     

The effect of dietary protein on the pathogenesis of acute ovine haemonchosis

Two experiments were conducted to examine the ifluence of dietary proteins on parasite establishment and pathogenesis in Finn Dorset/Dorset Horn lambs infected with Haemonchus contortus. The lambs were introduced to high (169 g) or low (88 g crude protein (CP) kg⁻¹ dry matter (DM)) protein diets at 3 months of age and infected 1 month later with 350 larvae kg⁻¹ body weight (BW). Blood and faecal smaples were collected for analysis and body weights recorded weekly. In the first experiments some of the infected lambs were killed 6 weeks after infection and the remainder 5 weeks later. In the second experimental all the infected lambs were killed 4 weeks after infection.

The results showed that lambs on a low protein diet were less able to withstand the pathogenic effects of infection with 350 H. contortus larvae kg⁻¹ BW than lambs given the higher protein diet. Thus mortality was greater in the low protein group and adverse clinical signs, such as inappetance, weight loss and oedema were osbserved more frequently. This group also had a more severe anaemia, hypoproteinaemia and hypoalbuminnaemia than the high protein group. In contrast, faecal egg counts, total daily faecal egg output and worm burdens were similar in all groups of infected lambs, indicating that the diets did not influence parasite establishment.     

Changes in the cortisol responses of lambs to tail docking, castration and ACTH injection during the first seven days after birth

Cortisol responses of Dorset and Scottish Blackface lambs were investigated at six ages between birth and seven days. There were four treatments: control handling and blood sampling (n = 52), tail docking (T) (n = 57), castration plus tail docking (CT) (n = 54), and intravenous adrenocorticotrophin (ACTH) injection (n = 60). Most lambs exhibited transient rises in plasma cortisol concentrations after treatment and the results in individuals were expressed as the area under the cortisol curve (integrated response). Postnatal changes in the integrated responses of control, T and CT lambs differed significantly between the two breeds; in Dorsets they increased markedly between four hours and one day and then decreased, whereas in Scottish Blackface lambs there were no significant changes. The cortisol responses of ACTH lambs decreased markedly between four hours and seven days in both breeds. The results shed light on postnatal changes in the activity of the hypothalamic-pituitary-adrenal axis and suggest for both breeds that the average increments in ACTH secretion caused by noxious stimuli increased markedly during the first one to three days after birth. Whether this reflected parallel increases in the levels of distress experienced by the lambs remains to be clarified.     

Maintenance of body temperature in the neonatal lamb: effects of breed, birth weight, and litter size

To survive, the newborn lamb must be able to maintain body temperature and to stand and move to the udder to suck colostrum to fuel heat production. The objective of this study was to investigate whether neonatal lambs showing slow behavioral progress to standing and sucking also have an impaired ability to maintain body temperature. The time taken to stand and suck after birth, rectal temperatures, and blood samples were collected from 115 newborn single, twin, and triplet lambs of 2 breeds, Scottish Blackface and Suffolk, which are known to show variations in their neonatal behavioral progress. Blood samples were assayed for thyroid hormones, known to be involved in heat production, and cortisol, which plays a role in tissue maturation before birth. In addition, colostrum samples were collected from the 56 ewes that gave birth to the lambs, and assayed for protein, fat, and vitamin contents. Heavy lambs (more than 1 SD above the breed mean), Blackface lambs, and singleton or twin lambs were quicker to stand and suck from their mothers than lightweight (more than 1 SD below the breed mean), Suffolk, or triplet lambs. Low birth weight lambs also had lower rectal temperatures than heavier lambs (P < 0.01), as did Suffolk compared with Blackface lambs (P < 0.001). Lambs that were slow to suck after birth had lower rectal temperatures than quick lambs, and this difference persisted for at least 3 d after birth. Within breed, heavy lambs had greater plasma triiodothyronine and thyroxine immediately after birth than light lambs. Blackface lambs had greater plasma triiodothyronine and thyroxine than Suffolk lambs but tended to have less cortisol. Colostrum produced by Blackface ewes had a greater fat content than that of Suffolk ewes (P < 0.001). Thus, lambs that are behaviorally slow at birth are also less able to maintain their body temperature after birth. Although part of their lower body temperature might be attributable to behavioral influences on thermoregulation, the data also suggest that physiological differences exist between these animals. These differences may be related to different degrees of maturity at birth.     

Reproductive traits of ewe lambs representing eight genetic types born in winter, spring, summer and fall

Crossbred ewe lambs of eight genetic types (Dorset X 3/4 Dorset, DD; Dorset X 3/4 Finn, DF; Finn X 3/4 Dorset, FD; Finn X 3/4 Finn, FF; Romanov X 3/4 Dorset, RD; Romanov X 3/4 Finn, RF; Romanov X Western, RW; and Western X Western, WW) were used to determine age and weight at conception, conception rate, ovulation rate, litter size and prenatal mortality. Each cross was represented in five different lamb crops born in winter, spring, summer and fall. High conception rates (greater than 88%) were obtained in all crops of ewe lambs, even in those born in June and exposed to rams the same year. Only Western ewe lambs born in June and exposed to rams in year of birth achieved low conception (59%). Ewe lambs born in October and missing the breeding season in the year of birth were more than 100 d older than ewe lambs born earlier in the calendar year and bred the same year. Prenatal mortalities varied widely (8 to 18%) among lamb crops, with management suspected to be a factor. Additive genetic effects in ovulation rate and litter size of the Romanov were similar to that of Finn. Romanov crosses (RF, RD, RW) conceived at the youngest age (226, 227, 231 d), demonstrating that Romanov is an early-maturing breed.     

Effects of breed and intake level on growth and feed efficiency in ram lambs

Effects of breed and intake level on growth and feed efficiency in ram lambs were tested with 52 Rambouillet, 46 Dorset and 53 Finnish Landrace (Finn) rams. Rams were individually fed at 100, 85 or 70% of ad libitum or at maintenance. The experimental diet contained 79% digestible dry matter (DM), 3.28% N and 2.95 Mcal metabolizable energy/kg DM. Rams were serially slaughtered every 35 d for 175 d. The efficiency of deposition of body weight, protein, energy and trimmed cuts was determined by breed and intake level over constant time, weight, fat and maturity intervals. Ranking of the breeds for feed efficiency depended upon both the interval and the criterion of evaluation. Efficiency of protein and trimmed cut gain was positively related to mature size in the time and weight intervals, but all differences in efficiency were small in the fat or maturity intervals. Gross energetic efficiency did not differ greatly among breeds in any interval. Dorsets appeared to have a somewhat greater propensity to fatten than the other breeds and to be less able to retain N at a fixed N intake. In the constant time interval, maintenance requirements were estimated to be 115 kcal/kg.75, and the estimated partial efficiencies of energy deposition in fat and protein were .49 and .26, respectively.     

Influence of dietary protein supply on resistance to experimental infections with Haemonchus contortus in Ile de France and Santa Ines lambs

The effect of Haemonchus contortus infection in sheep fed with a moderate and high protein content diet was evaluated in two breeds of sheep. Forty-eight Ile de France and Santa Ines lambs were maintained indoors since birth, in worm-free conditions. The lambs were allocated after weaning in four groups of six animals per breed, which were either infected or remain uninfected and given access to either a moderately or highly metabolizable protein diet. The moderately and highly metabolizable protein diets were calculated to supply 75 and 129 g metabolizable protein per kg of dry matter (MP/kg DM), respectively. The infection consisted of a trickle infection with 300 infective larvae, three times a week, for 12 weeks. Significant differences were observed for mast cell, globule leukocyte and eosinophil counts in the abomasal mucosa of the infected groups compared to the control of both breeds (P<0.05), regardless of the diet supplied. Significantly higher IgA anti-L5 antibody was detected in the infected Santa Ines groups than in the infected Ile de France groups (P<0.05). Increased metabolizable protein supply resulted in larger body weight gain and higher packed cell volumes for both breeds (P<0.05). Both breeds showed an increased ability to withstand the pathophysiological effects of H. contortus infection when given access to the highly metabolizable protein diet. However, increased metabolizable protein supply resulted in reduced worm burdens in Santa Ines lambs but not in the Ile de France lambs (P<0.05). The present results show that the increase in protein content in growing lamb diets may benefit resistance and resilience to gastrointestinal parasites but that these benefits may vary among breeds.     

舍饲绵羊产后56 d内乳成分变化规律研究

随着人民生活水平提高和膳食结构调整,绵羊奶必将受到人们的青睐.选取甘肃肉用绵羊新品种群、无角陶赛特和特克塞尔3个品种各8只母羊,对产后1～56 d泌乳理化性质变化进行研究,结果表明：3个品种乳成分及物理性质在第1～3 d变化最为明显,其中乳蛋白含量、非脂固形物含量和酸度3项指标呈现出前期快速下降,中期下降减缓,后期缓慢上升;乳糖指标则呈现出缓慢的前期上升,后期下降的趋势,对选取的3个品种初乳中蛋白、乳脂和可溶性固形物含量等指标对比,依次下降,乳糖含量和密度特克塞尔最高.常乳中除密度外3个品种间差异不显著（P＞0.05）.这为绵羊早期断奶和补饲提供了基础数据.     

Experimental Haemonchus contortus infection in three breeds of sheep

Nine- to 10-month-old Florida Native, St. Croix and Dorset/Rambouillet sheep were infected with Haemonchus contortus. The primary infection was terminated by anthelmintic treatment 9 weeks later and animals were then reinfected with H. contortus. Dorset/Rambouillet sheep showed higher fecal egg counts and decreased packed cell volumes and plasma protein levels compared with the other two breeds during the primary infection. However, no breed differences were found in total worm burdens in either primary or secondary infection. Differences between breeds were also not detected in lymphocyte responsiveness to parasite antigen, H. contortus specific mucosal antibody levels, numbers of abomasal mast cells and globule leukocytes or abomasal histamine levels.     

Bluetongue disease in Swiss sheep breeds: clinical signs after experimental infection with bluetongue virus serotype 8

Clinical disease of bluetongue (BT) in sheep may differ depending on breed, age and immunity of infected sheep and may also vary between serotype and strain of BT virus (BTV). Since there are no data available on the susceptibility of Swiss sheep breeds for BT, we performed experimental infection of the 4 most common Swiss sheep breeds and the highly susceptible Poll Dorset sheep with the BTV serotype 8 (BTV-8) circulating in Northern Europe since 2006. Clinical signs were assessed regarding severity, localisation, progression and time point of their appearance. The results clearly show that the Swiss sheep breeds investigated were susceptible to BTV-8 infection. They developed moderate, BT-characteristic symptoms, which were similar to those observed in Poll Dorset sheep. Regardless of breed, the majority of infected animals showed fever, swelling of the head as well as erosions of the mouth and subcutaneous haemorrhages.     

Inactivated bluetongue virus vaccine in lambs: Differential serological responses related to breed

A mixed breed flock of lambs, consisting of Suffolks, Hampshires, Columbias and Finnish breeds, were vaccinated with binary ethylenimine inactivated bluetongue virus (BTV) serotypes 11, 17 and a mixture of 11 and 17 in aluminum hydroxide. Agar gel precipitin antibodies were used as an indicator of immunity. Sero-conversion of Hampshires and Suffolk lambs was poor at 43% as compared to 84% in the Columbia and Finn lambs. These results indicate a breed difference in immunological response to inactivated BTV vaccine.     

Year-round breeding of crossbred Dorset or Finnish landrace ewes using a synthetic light regimen

A group of crossbred Dorset or Finnish Landrace ewes maintained under a synthetic light regimen (Light Treatment, 4 mo long days - 16 h light, 4 mo short days - 8 h light) and exposed to rams every 8 mo (January 1, September 1, May 1) was compared for lamb production over a period of 4.5 yr with two other comparable groups under natural daylight conditions, one exposed to rams once a year in the fall (Control I) and the other every 8 mo (Control II). Conception rates across breed type of ewe were 92% for Control I, 66% for Control II and 83% for Light Treatment ewes. Conception rates for May breedings only were 16% in Control II and 88% in Light Treatment ewes. Prolificacies of crossbred Finn ewes were higher (P less than .05) than those in crossbred Dorset ewes of Control I (258 vs 193%), Control II (187 vs 165%) and Light Treatment (238 vs 163%). The annual production at lambing from the crossbred Finn and Dorset ewes in Control I was 251 and 206 lambs/100 ewes exposed to rams, respectively. Corresponding productions were 231 and 178 for Control II and 296 and 211 for Light Treatment ewes. Mortality of lambs from the crossbred Finn ewes (27%) was higher (P less than .01) than that from the crossbred Dorset ewes (12%). Annual attrition of the crossbred Dorset ewes in Control I, Control II and Light Treatment groups was 5.2, 5.4 and 5.4%, respectively. Corresponding percentages of the crossbred Finn ewes were 7.0, 8.8 and 11.2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lamb production performance of 14 sire breeds mated to New Zealand Bomney ewes

From an extensive series of trials involving approximately 15 000 Romney ewes mated with 435 rams, provisional results are presented on the comparative performance of 14 sire breeds for lamb meat production. The breeds, each represented by ten or more rams, were Southdown, Suffolk, South Suffolk, Hampshire, Dorset Down, South Dorset Down, Poll or Horn Dorset, Border Leicester, English Leicester, Ryeland, Cheviot, Lincoln, Merino and Romney.Important differences exist between sire breeds in progeny survival, with the Southdown being best and the Romney poorest. Progeny of long-wool sires, and particularly the Lincoln, clip more wool at post-weaning shearing than of the Down breeds, which exhibit quite small variation.Sire breeds vary in average live-weight and carcass growth of their progeny, the Suffolk, Hampshire and Dorset breeds producing the heaviest and Merino and Romney the lightest lambs. In terms of lamb live-weight or carcass production per Romney ewe mated, Romney, Merino, Lincoln, Ryeland, Cheviot and English Leicester sires are inferior to the Southdown while Dorset, Suffolk, South Suffolk and Dorset Down are superior.Within any breed, wide differences exist between progeny growth rates of the best and poorest sires, emphasising the importance of sound selection of rams and of adequate genetic sampling in breed comparisons.     

A comparison of Dorset and Finnish Landrace crossbred ewes

Data from 644 exposures and 552 lambings were used to analyze reproductive traits of 1/2-Finnish Landrace, 1/2-Dorset ewes (1/2 Finn); 1/4-Finnish Landrace, 3/4-Dorset ewes, (1/4 Finn) and Dorset ewes. Ewes were exposed to Hampshire or Suffolk rams for spring lambing from 1973 to 1978. The analytical model included fixed effects of ewe birth year (EBY), ewe breed (BR), lambing year within EBY and EBY X BR interaction and random effects of ewe within EBY and BR. Conception rate differed (P less than .01) for 1/2-Finn (.94), 1/4-Finn (.88) and Dorset (.80) ewes. Litter size was highest (P less than .01) for 1/2-Finns (1.97), followed by 1/4-Finns (1.74) and Dorsets (1.44). The 1/2-Finn ewes ranked first for number and weight of lambs weaned, and for number and weight marketed as feeder lambs. Birth weights were heavier (P less than .001) for lambs with Dorset dams (3.88 kg) than for lambs with 1/4-Finn (3.24 kg) or 1/2-Finn (3.08 kg) dams. Preweaning average daily gains and adjusted 90-d weights were also larger (P less than .001) for lambs with Dorset dams (.26 kg/d and 28.3 kg, respectively) than for lambs with 1/4-Finn (.24 kg/d and 25.4 kg) or 1/2-Finn (.24 kg/d and 25.1 kg) dams. However, Dorset ewes lambed an average of 10.5 d later than Finn-cross ewes, and actual weaning weights (unadjusted for age) did not differ significantly among lambs from Dorset (27.2 kg), 1/4-Finn (26.9 kg) and 1/2-Finn ewes (26.7 kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

The development of a new breed of sheep in Colombia

A new breed of sheep has been developed in Colombia by crossing Scottish Blackface rams with the indigenous Criolla ewes and then interbreeding the progeny, with selection based on performance. It has been given the name Manchada Paramuna. The breed has been developed to provide the small producer (campesino) with a breeding ewe which has a high level of fertility, a good fleece, and which produces lambs with high survival rate and good growth rate.     

Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: IV. Survival, growth, and carcass traits of F1 lambs

The objectives of this study were to estimate effects of sire breed (Dorset, Finnsheep, Romanov, Texel, and Montadale), and dam breed (Composite III and Northwestern whiteface) on survival, growth, carcass, and composition traits of F1 lambs. Effects of mating season (August, October, and December) were estimated for survival and growth traits. Data were collected on 4,320 F1 lambs sired by 102 purebred rams over 3 yr. Birth weight was recorded on all lambs, and subsequent BW were adjusted to 56 (weaning), 70, and 140 d of age (n = 3,713, 3,654, and 3,579 observations, respectively). Survival of dam-reared progeny (n = 4,065) to weaning was recorded. Each year, wethers from October matings were slaughtered in three groups at 25, 29, and 33 wk of age to obtain carcass data (n = 546). In addition to standard carcass traits, resistive impedance measurements were recorded on the warm carcass to predict lean mass. Dam breed (P = 0.37) did not influence lamb survival to weaning, but sire breed (P < 0.05) was important. Romanov-sired lambs excelled in survival rate to weaning (94.1%), followed by Finn-sheep (93.0%), Texel (90.7%), Dorset (90.0%), and Montadale (89.1%) sired progeny. Lower (P < 0.01) postweaning growth rate was observed for Texel (267 g/d) and Finnsheep (272 g/d) sired progeny than for Dorset (285 g/d), Montadale (282 g/d), and Romanov (278 g/d) sired progeny. Sire breed and dam breed were generally significant for most carcass traits. Breed differences in distribution of carcass fat and carcass shape were detected; however, carcass composition was similar for all sire breeds when compared at a constant carcass weight. When evaluated at a constant 12th-rib fat depth, carcasses of lambs from Finnsheep, Romanov, and Texel sires produced 1 to 1.5 kg less (P < 0.001) predicted lean mass per lamb than carcasses of lambs from Dorset and Montadale sires. These experimental results provide information about the direct breed effects for survival, growth, and carcass traits of these breeds and their potential use in crossbreeding systems.     

Changes in food intake and circulating leptin due to gastrointestinal parasitism in lambs of two breeds

A reduction in food intake is a prominent feature of many infectious diseases. However, the underlying mechanisms of parasite-induced anorexia in sheep are poorly understood. Here, we tested the hypotheses (a) that the degree of parasite-induced anorexia in lambs is influenced by their growth potential and (b) that nematode infection results in elevated plasma leptin concentration in lambs. The hypotheses were tested with Suffolk x Greyface (S) and Scottish Black-face (B) lambs that are known to differ in their growth potential (S lambs are of greater growth potential than B lambs). During a primary parasite infection, 24 out of 48 lambs per breed were trickle-infected with 7,000 infective Teladorsagia circumcincta larvae per day, 3 d/wk, for a period of 12 wk (experiment I). The lambs were then dewormed, and after a 2-wk interval, half of the 24 lambs per breed that were previously infected were reinfected for another 12 wk with the same parasite and dose as used in the primary infection (experiment II). In both experiments, infected lambs were fed grass pellets for ad libitum intake, whereas noninfected lambs were fed grass pellets for either ad libitum or restricted intakes. The S lambs were more susceptible than B lambs to nematode infection, as judged from the differences in fecal egg counts (P = 0.007). Parasitized lambs of the more susceptible breed (S) showed anorexia [i.e., a decrease in intake of 13% compared with uninfected controls (P = 0.01)], whereas no significant reduction in food intake was observed in lambs of the more resistant breed (B). Reexposure to nematode infection of previously infected animals tended to result in renewed anorexia in S lambs but not in B lambs (P = 0.08) in a similar extent as during primary infection. Plasma leptin concentrations did not differ between ad libitum-fed infected and control lambs but were greater in infected than in noninfected lambs at a similar level of food intake during both the primary (P = 0.02) and the secondary parasitic infection (P = 0.004) in both breeds. The results show that leptin may be involved in the response of lambs to infection but that it is unlikely that leptin alone is responsible for the parasite-induced anorexia in lambs.     

Breed group differences in testicular growth patterns in spring-born ram lambs

Three groups of spring-born ram lambs were used to assess breed group differences in testicular growth patterns through 5 mo of age. Group 1 included 20 3/4-Finnish Landrace (Finn), 1/4-Rambouillet rams and 31 1/8-Finn, 7/8-Rambouillet rams. Group 2 included 23 3/4-Finn, 1/4-Dorset rams and 19 1/8-Finn, 7/8-Dorset rams. Group 3 included 21 black-faced (BF) rams (six Hampshire and 15 Suffolk) and 46 whitefaced (WF) rams (nine Dorset, 20 Barbados Blackbelly X Dorset, 10 Finn X Dorset and six Dorset X Finn). Scrotal circumference (C) was measured at 19, 43, 72, 100, 128 and 153 d in Group 1; at 20, 48, 76, 93 and 153 d in Group 2 and at 40, 60, 81, 103, 124 and 158 d in Group 3. Breed group X age interaction was tested to assess breed group differences in testicular growth patterns, and logistic curves were used to describe increases in scrotal circumference with age. In Group 1, 3/4-Finn and 1/8-Finn rams were similar in estimated final scrotal circumference at 150 d of age (260 and 259 mm, respectively), but rapid testicular growth began earlier in 3/4-Finn rams. The estimated age at which the growth rate in scrotal circumference was maximum was 81 d for 3/4-Finn rams and 93 d for 1/8-Finn rams. No differences were observed in testicular growth in Group 2 rams. However, in Group 3, smaller WF rams matured more rapidly than larger BF rams. Growth in scrotal circumference was most rapid at 99 d in BF rams and 88 d in WF rams. Within WF rams, Barbados Blackbelly X Dorset and Finn X Dorset rams matured earlier than Dorsets. In all groups, the primary breed difference was associated with age differences during the period of rapid testicular growth.