Additive and nonadditive genetic effects on lifetime yields of milk and milk components and lifetime profitability were estimated from 5070 cattle in a Holstein pureline, an Ayrshire-based pureline, and 10 crossbred groups of these purelines. Lifetime yields of milk, fat, protein, and lactose and lifetime milk value and annualized discounted net returns were analyzed. Lifetime yields, lifetime milk value, and annualized discounted net returns of the Holstein x Ayrshire-based line F1 and an F1 x (F1 x F1) cross were not significantly different from those for the Holstein pureline. Net reproductive rate for F1 females was 9% greater than that of contemporary Holsteins. The Holstein pureline was superior to the Ayrshire-based pureline for direct additive genetic merit for all traits. Heterosis for the lifetime traits ranged from 16.6% for lifetime milk yield to 20.6% for annualized discounted net returns. Cytoplasmic maternal effect on annualized discounted net return was significant and favored the Ayrshire-based line. Potential economic benefit may derive from development of a crossbred cow that is superior to Holsteins. Maximum exploitation of additive and nonadditive genetic effects on lifetime yields and profitability appears to favor a rotational crossbreeding system with two breeds.

Early first lactation data from 2230 cows of five research herds of Agriculture Canada were used to study the interactions of genetic line by concentrate level, and sire by concentrate level and to estimate breeding values of sires. The genetic lines were defined as Holstein (H), Ayrshire (A), and H × A or A × H (C). The interactions of sire by concentrate level were studied separately using progeny of five different mating groups: G1, H sires mated to H cows; G2, H sires mated to H, A and C cows; G3, A sires mated to A cows; G4, A sires mated to H, A and C cows; and G5, C sires mated to C cows. The interactions of genetic line by concentrate were significant (P < 0.05) for 56- to 112-d milk yield (MY112), corrected 56-to 112-d milk yield (CMY112) and feed efficiency (EFMY112 = MY112/TDN consumption). H and C cows produced more milk and were more efficient than A cows when fed high levels of concentrate. The H cattle possess a greater capacity to convert the concentrate into milk, while A cattle reach maximum milk production earlier than H cattle. The interactions of sire by concentrate were statistically significant for MY112, EFMY112 and CMY112 in G1 (P < 0.01), and G2 (P < 0.01). The breeding values of sires for MY112 were estimated using BLUP for all of the H line (BLUP-T), for half of the population consuming low amounts of concentrate (BLUP-L) and for the other half consuming high amounts (BLUP-H). A significant reranking of sires was found among the three groups. Key words: Genotype × environment interaction, milk production, efficiency, breeding value, dairy cattle

Heritabilities, genetic and phenotypic correlations among growth, forage consumption, and BW changes of heifers and feed consumption, BW changes, and yields of first lactation cows were estimated. Data were from 1266 Holstein progeny of 74 sires born from 1972 to 1985 at three Agriculture Canada research herds. Heavier heifers at 26 wk consumed more feed from 26 to 34 wk than smaller heifers but gained the same BW. The BW gain and feed consumption heritabilities were .17 and .23, respectively; genetic correlation was .44, and phenotypic correlation was .27. During first lactation, feed intake from 8 to 16 wk and measures of milk yield are very tightly intercorrelated both phenotypically and genetically (.78 to .98). Precalving BW gain and BW at calving were genetically uncorrelated with measures of milk yield (-.09 to +.05). Loss of BW during the first 8 wk of first lactation was moderately heritable (.29) and correlated genetically and phenotypically with measures of milk yield in early lactation (.32 to .39) and feed consumption (.26). From 8 to 16 wk, average BW changes were small and had low heritability and weak phenotypic correlations with measures of milk yield or feed intake. The BW at 26 wk and BW gain from 26 to 34 wk were very poor indicators of early first lactation milk yield. Heifer feed intake was weakly correlated phenotypically (-.07 to .16) but moderately genetically correlated (.17 to .23) with early first lactation milk yield and feed consumption.

Early part records for milk yield and feed consumption of 2230 first lactation purebred and crossbred dairy cows were analyzed to evaluate various measures of feed efficiency. Corrected milk yield was estimated by adjusting the second 8 wk of milk yield for differences in weight of TDN consumed during wk 9 to 16, percentage of TDN derived from concentrate, and BW.75. Corrected milk yield is an estimate assuming that cows are the same size and consume the same amount of feed. Hence, it represents an expression of feed efficiency. Net feed efficiency, gross efficiency, corrected milk yield, and wk 9 to 16 milk were analyzed simultaneously. Coefficient of determination for net efficiency (.51) and gross efficiency (.72) were lower than that of milk (.82), whereas corrected milk yield had a coefficient of determination similar to that of milk. Hence, the use of ratios to define feed efficiency was less accurate than using corrected milk yield. Effects of genetic groups, stations, season of freshening, year of freshening, and heterosis were similar for gross efficiency and corrected milk yield, but different from those for milk. Therefore, corrected milk yield performed the same function as feed efficiency with higher accuracy.

Two experiments were performed in order to determine the best method for evaluation of weight-gaining ability of lambs. Lambs on unrestricted access to feed and water (full fed) gained 2–3% of live weight on the following day while lambs deprived of feed and water (fasted) overnight gained 0–3%. However, full fed lambs lost 5–10% of live weight when fasted overnight, or gained 7–10% if full fed at night. In 38 to 43% of the lambs fasted overnight, weights measured at successive weigh days were identical, a higher proportion than in lambs subjected to other treatments. Estimates of intra-class correlations between weights on successive days in lambs fasted overnight prior to weighing, or full fed until weighing, ranged from −8 to 0%. Corresponding estimates for lambs fasted overnight followed by full feeding, or vice versa, were highly variable, due to differences in weight of gastro-intestinal and urinary tract (‘fill’) contents and ranged from 8 to 60%. There appears to be no justification for weighing on successive days when a single accurate weighing equals the average weight. It was concluded that overnight withdrawal of feed and water before weighing reduced significantly the variation in body weight associated with retention of feed and water, facilitating a more precise assessment of lamb's growth potential.

Three estimators of intrapopulation genetic change were used to quantify response to selection for protein yield in first lactations, of Holsteins from three herds of the Research Branch of Agriculture Canada. Selection began in 1972 and continued through 1985. For the first 3 yr (1972 to 1974), foundation cows were mated by AI to young bulls from the foundation herds and to progeny-tested bulls available in US and Canadian AI units. Progeny-tested bulls produced in this closed herd selection project were not available for selection before 1978. A mixed model analysis based on sire merit revealed an apparent curvilinear response to selection with the most pronounced improvement occurring during the last 5 yr. Sons produced by progeny-tested bulls selected within the project in 1978 and 1979 were superior to the progeny-tested bulls from AI units used in the foundation matings. This sire superiority for protein, milk, and fat yield was 7.3, 193.6, and 7.1kg, respectively. Genetic trend in the cow population was estimated by two regression procedures. Estimates of annual gain for protein yield were 1.0 and 2.2kg and protein equivalent to .7 and 1.8% of mean yield. Corresponding estimates of correlated responses were 45.9 and 68.6kg milk and 1.3 and 2.3kg milk fat.

Data from 889 cows at five research stations of Agriculture Canada were used to study the effects of alpha s1-casein, beta-casein, kappa-casein, and beta-lactoglobulin loci on herdlife and total yield over fixed parities (one, two, and three parity) and to a fixed age (36, 48, and 61 mo). Actual yields of all cows were utilized to compute total milk regardless of lactational length. The model consisted of station, breed, year of birth, season of birth, and milk protein types with age at first calving as a covariate. Of the four milk protein types studied, only the kappa-casein locus had significant effects on fixed parity and fixed age total milk and herdlife. Cows with BB kappa-casein type outproduced those with AB or AA kappa-casein types in three parity total milk by 963 and 1657 kg, respectively. Considering total milk accumulated up to 61 mo of age in life, cows with BB kappa-casein type outperformed their counterparts with AB or AA kappa-casein types by 1050 and 1923 kg, respectively. Complete replacement of A by B allele at kappa-casein locus would result in an increase of 1657 kg in three parity total milk and an increase of 1923 kg in 61-mo total milk. The moderate gene frequency of kappa-casein B allele in the current dairy population can be increased to improve lifetime total milk to the benefit of the dairy industry.

Feed efficiency was examined from approximately 3200 records of feed intake, milk yield, weight and weight change during the second eight weeks of first lactation on Holstein (H line), Ayrshire based (A line) and crossbred (C line) cattle. Herd, year-season and age at first calving with either genetic line or original breed source additive, heterotic and maternal effects were included in models. Heterotic and maternal effects on milk yield, TDN consumption and feed efficiency were generally unimportant when initial weight, weight change and milk yield or TDN covariates were considered. Line (A, H and C) and breed source additive effects within line were generally significant (P < 0.05). Efficiency was highly correlated phenotypically (0.64) with milk yield but only mildly correlated with measures of feed intake (0.13, 0.38). The negative correlation of efficiency with initial weight (−0.13) and weight change during the trial (−0.15) indicated that the larger animals or animals which gained more weight use a higher proportion of feed energy for maintenance requirements and growth than lighter animals. The strong correlations (0.63, 0.81) between milk yield and consumption arose in part from feeding concentrates according to milk production and made appropriate analyses difficult. Adjusted for covariates, Canadian (CH) and American (USH) Holsteins were the highest producers followed by Norwegian Red (NR), Agriculture Canada Holsteins (ACH), Ayrshires and Brown Swiss. North American Ayrshires (NAA) consumed the least TDN, adjusted for covariates, with Holsteins intermediate and Brown Swiss highest. In general, Ayrshires were more efficient than Holsteins. Feed efficiencies of NAA, Finnish Ayrshire and NR were superior to those of ACH with other genetic groups intermediate. Key words: Genetic, feed efficiency, lactation, cattle

Brahman-British beef cattle crosses in Canada (F1 hybrids) out-gained contemporary Herefords under both winter and summer range conditions. Brahman × Hereford, Brahman × Angus and Brahman × Shorthorn steers marketed off grass at 2.5 yr of age surpassed Herefords by 61 – 64 kg in cold carcass weight, 3.9 – 4.8% in dressed carcass yield, and 4 – 6 cm2 in longissimus dorsi area per 250 kg of carcass. The 1/4-Brahman progenies from matings of Hereford bulls with F1 cows did not differ significantly from Herefords in year-long postweaning gain, either under Alberta range conditions or under summer grazing and limited winter feeding conditions at Ottawa, Ontario. Hereford × (Brahman × Hereford) backcross calves gained less than Herefords but averaged 16 kg heavier in cold carcass weight because of greater initial (weaning) weight and a higher dressing percentage. There was no difference between the crosses (F1 hybrids and back-crosses) and Herefords in carcass grade. The major benefit of the Brahman-British cattle crosses resulted from the superior performance of the F1 hybrids, expressed as a marked superiority in growth rate of the F1 steers and heifers and a greater weight-for-age of the 1/4-Brahman progenies of F1 cows. Key words: Brahman, Hereford, Angus, Shorthorn, crossbreeding

Plasma insulin and growth hormone (GH) were measured in 62 monensin-treated lambs and 59 control lambs from four experiments that were conducted to determine the effect of monensin treatment on average daily gain (ADG) and gain to feed ratio (G:F). Plasma GH concentrations were lower in lambs that received monensin (P < 0.05–0.01). The effect was greater in ram than in ewe lambs (P < 0.03). Monensin treatment started when lambs were only a few weeks old and resulted in a more rapid GH response than when older lambs were treated. In some, but not all, of the experiments the lower plasma GH concentrations occurred in conjunction with an increase in ADG and an apparent increase in G:F. Monensin had little effect on plasma insulin concentrations. Key words: Lambs, monensin, growth hormone, insulin

Dairy heifers were randomly divided into two treatment groups. One group of 253 heifers was bred at first estrus after 350 d of age and the second group of 249 heifers after reaching 462 d of age. Feeding and management practices were identical; groups differed only in age at first breeding. This report compares production of second and third lactations, reproductive traits observed during first and second lactations, and lifetime performance. Comparisons of heifer reproduction and first lactation production were reported earlier. Although the 462-d breeding age group of heifers had slightly better first lactation performances than the 350-d breeding age group, these advantages were not carried over to second and third lactations. No significant differences existed in three-parity performance between the two breeding groups. The 350-d breeding group had longer 61-mo productive life (730 vs. 623 d), produced greater 61-mo total milk (10,693 vs. 9218kg), and yielded more milk per day of 61-mo herdlife (6.8 vs. 5.9kg). A reduction of 1 mo in age at first calving would increase three-parity and 61-mo total milk by 427 and 554kg, respectively. Results from this study suggest that early breeding is a viable and practical approach to improve profitability for the dairy industry.

Factors affecting survival to first and second calving and successful completion of a > 168-day first lactation were assessed in 3075 purebred and crossbred dairy heifer calves. Growth, disease, frequency, reproduction, calving, udder and lactation traits were examined in females of a breeding project conducted jointly at five research stations (herds) of Agriculture Canada. Losses included mortalities and non-discretionary culling. About 0·23 of potential heifers were culled or died before first calving, and 0·25 of those calving once did not calve a second time. Results from retrospective selection index and stepwise linear logistic analyses showed that predictability of culling prior to 308 days post partum was poor. With few exceptions, survival rates from birth to 82 weeks varied among herds (P < 0·001) and among lines (P < 0·05). Heterosis for the probability of completing a lactation and of survival to second calving was significant (P < 0·05) and positive (0·05 to 0·09). Heavier heifers were more likely to survive to first calving. Sire's estimated breeding values (SEBV) for milk yield and fat, protein and lactose concentration were not important in predicting survival to first calving. SEBV lactose was negatively associated with survival after first calving as predicted from data available at most preceding stages of life. An age greater than 82 weeks at last insemination was associated with a lower probability of survival to first and second calving (P < 0·001). Cows which conceived for a second gestation and subsequently aborted had a lower probability of survival to second calving than cows which did not abort (0·57 v. 0·76, P < 0·01). The only continuous traits with large effects on survival or the probability of completing a first lactation were days to last insemination (a measure of fertility) and milk yield. It was concluded that (1) there is considerable scope for improved management to increase survival in early life by prevention of calfhood diseases; (2) losses in early life do not bias sire evaluation on first lactation records; (3) improved reproductive success would greatly enhance overall survival rates; and (4) crossbreeding could have a large impact on overall herd profitability through increased survival.

The proportional hazards model with censoring was used to assess the effects of breeding value, disease, calving, size, and udder and lactation traits on length of herdlife of 3881 heifers in five herds. Data were recorded over 10 yr from three lines: a Holstein line, an Ayrshire-based line, and a crossbred line. Influences on survival were assessed from data collected at birth, 34, 50, and 82 wk, first freshening, and at 112 and 308 d postpartum. Median estimated herdlife (age at 50% culling) was 3.9 yr for animals alive at first freshening and increased to 4.3 yr for those that completed a first lactation (308 d postpartum). Herds differed greatly in the pattern of culling after freshening. Crossbred females had 21 wk longer median estimated herdlife than the mean of the purelines at 308 d postpartum. Individual milk yield was positively associated with longevity and had the greatest impact on length of herdlife. Abortion and fertility measured as days to last insemination were negatively associated with length of herdlife. Large heifers tended to have increased longevity. High feed intake postpartum was associated with reduced length of herdlife. Objective measures of conformation, which included measurements of the udder, were not important in determining herdlife.

ABSTRACTFactors affecting survival to first and second calving and successful completion of a > 168-day first lactation were assessed in 3075 purebred and crossbred dairy heifer calves. Growth, disease, frequency, reproduction, calving, udder and lactation traits were examined in females of a breeding project conducted jointly at five research stations (herds) of Agriculture Canada. Losses included mortalities and non-discretionary culling. About 0·23 of potential heifers were culled or died before first calving, and 0·25 of those calving once did not calve a second time. Results from retrospective selection index and stepwise linear logistic analyses showed that predictability of culling prior to 308 days post partum was poor. With few exceptions, survival rates from birth to 82 weeks varied among herds (P < 0·001) and among lines (P < 0·05). Heterosis for the probability of completing a lactation and of survival to second calving was significant (P < 0·05) and positive (0·05 to 0·09). Heavier heifers were more likely to survive to first calving. Sire's estimated breeding values (SEBV) for milk yield and fat, protein and lactose concentration were not important in predicting survival to first calving. SEBV lactose was negatively associated with survival after first calving as predicted from data available at most preceding stages of life. An age greater than 82 weeks at last insemination was associated with a lower probability of survival to first and second calving (P < 0·001). Cows which conceived for a second gestation and subsequently aborted had a lower probability of survival to second calving than cows which did not abort (0·57 v. 0·76, P < 0·01). The only continuous traits with large effects on survival or the probability of completing a first lactation were days to last insemination (a measure of fertility) and milk yield. It was concluded that (1) there is considerable scope for improved management to increase survival in early life by prevention of calfhood diseases; (2) losses in early life do not bias sire evaluation on first lactation records; (3) improved reproductive success would greatly enhance overall survival rates; and (4) crossbreeding could have a large impact on overall herd profitability through increased survival.

Data on 3957 heifers from the Holstein H line, Ayrshire-based A line, and C line (crossbreds between H and A lines) were used.Growth, feed consumption, and feed efficiency from 26 to 34 wk were examined.The full model included the fixed effects of herd, year of birth, season of birth, and additive, maternal, and heterotic genetic effects with 26-wk weight as a covariate.Heterotic and maternal effects were not significant.Adjusted for the 26-wk weight covariate, H line heifers gained 3 kg more than A line heifers with C line heifers intermediate.Adjusted for 26 and 34-wk weight covariates, H line heifers ate 2 kg less TDN than A line heifers and, hence, were more efficient.Correlations among traits were estimated using the residual variance-covariance matrix from the full model.Body weight at 34 wk was correlated with 26-wk weight (r = .88)but essentially independent of rate of gain (r = .02).It was correlated with feed consumed (r = .51)and negatively associated with gain/feed consumed (r = -.25).Gain was correlated (r = .84)with gain/feed consumed but mildly so (r = .28)with feed consumed.Feed con-

A total of 890 heifers was used to study the effects of four milk protein loci (alpha S1-casein, beta-casein, kappa-casein, and beta-lactoglobulin) on heifer growth and reproduction. The additive effects of gene substitutions at the four milk protein loci were significant only in 4 of 56 cases for all traits studied. Dominance effects at alpha S1-casein, beta-casein, and kappa-casein loci were not significant for any traits except beta-casein locus on body weight at first calving. Heifers with AB type of beta-lactoglobulin showed greater body weights and measurements and gestation length than the AA or BB type, indicating an overdominance effect. Heifers with AB type of beta-lactoglobulin were significantly younger at first conception and at first freshening and had fewer number of days from first service to conception than the AA or BB type, indicating underdominance effect. Thus, beta-lactoglobulin locus shows overdominance, underdominance, or no dominance, depending upon the traits considered. The four milk protein loci contributed more dominance variance than additive variance to total phenotypic variance. This might account for the existence of milk protein polymorphism in the cattle population. The combined genotypes of the four milk protein loci showed significant effects on 2 of 14 traits studied.

Weekly milk yields of 1022 Holstein heifers from 61 sires were used to derive coefficients of the lactation curves using modified gamma and inverse polynomial functions. The natural logarithm of a modified gamma function was ln(yn) = ln (a) + b ln (n) + cn + u sin (x) + v cos (x), where a, b, c, u, and v are coefficients to be estimated; n is the day of lactation; and x is the day of year. Estimates of a, b, and c were combined to define persistency [-(b + 1) ln c], week of peak yield (b/c), and peak yield [a(b/c)be-b]. The inverse polynomial function was n/yn = A0 + A1n + A2n2, where A0, A1, and A2 are coefficients to be estimated. Variance and covariance components for the coefficients of the lactation curve were estimated by the multitrait restricted maximum likelihood method using canonical transformation. Heritability estimates were ln (a) .11, b .07, c .04 u .01, v .04, A0 .28, A1 .26, A2 .21, persistency .21, week of peak .18, peak yield .23, and 308-d milk yield .41. Genetic correlations indicated that selection for faster rate of increase to peak production would result in higher 308-d milk production, higher peak yield, and greater persistency.

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.