de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The objective of this study was to compare the estrus synchronization efficiency of PGF2alpha in cattle (n = 470) not having shown estrus for 4 (D4 treatment) or 7 d (D7 treatment) after onset of the breeding season. The physiological status of crossbred Charolais cows was studied, and their reproductive performance was compared to that of Shorthorn-Hereford cows. The percentage of cows in estrus during the 7 d prior to PGF2alpha treatment was superior (P < 0.01) to that observed during the 4 d preceding PGF2alpha. The daily rates of estrus were similar during the 2 periods. For both the Shorthorn-Hereford (87.8 vs 74.7%; P < 0.03) and crossbred Charolais (87.8 vs 66.3%; P < 0.005) females, the estrus synchronization rate during the 5 d post PGF2alpha was higher in treatment D7 than in the D4 treatment. Therefore, for both Shorthorn-Hereford (92.8 vs 81.4%) and crossbred Charolais (93.1 vs 75.0%) the D7 program permitted insemination in 12 d (before and after PGF2alpha) of a higher percentage (P < 0.01) of females than the D4 program did in 9 d. The intervals PGF2alpha to estrus and their variances were similar for both treatments. The conception rate of Shorthorn-Hereford was the same whether they were inseminated after spontaneous (73.4%) or PGF2alpha-induced estrus (D4 treatment: 78.5%; D7 treatment: 72.2%). However, crossbred Charolais cows inseminated after a PGF2alpha-induced estrus in the D4 treatment had a fertility rate (50.9%) slightly inferior (P < 0.07) to that of cows inseminated after spontaneous estrus (70.1%) or after PGF2alpha-induced estrus in the D7 treatment (67.4%). The reproductive performances of multiparous Shorthorn-Hereford and crossbred Charolais were similar in treatment D7; however, in the D4 treatment, the conception rate of Shorthorn-Hereford was higher than that of crossbred Charolais (81.0 vs 42.9%; P < 0.002). Primiparous crossbred Charolais in the D4 treatment had a slightly lower (P < 0.10) synchronization rate (48%) than nulliparous (71%) and multiparous crossbred Charolais (78%). In contrast, the reproductive performances of nulliparous, primiparous and multiparous crossbred Charolais were similar in the D7 treatment. These results indicate that the efficiency of PGF2alpha to synchronize estrus is greater when the estrus detection period increases from 4 to 7 d before PGF2alpha. Only in the D7 treatment was the fertility rate of crossbred Charolais similar to that of Shorthorn-Hereford.

Fifty-seven black and white male dairy calves, reared from 48 to 222 kg liveweight, were used to study the effects of photoperiod and feeding whole maize (75%; WM), whole barley (80%; WB) or rolled barley (80%; RB) based diet after weaning. Photoperiod treatments were 10 h of light (L):14 h of dark (D), 16L:8D, 10L:14D for 6 weeks then followed by 16L:8D, or 16L:8D for 6 weeks then followed by 10L:14D. During weeks 17 and 20, 30 calves of uniform weight, ten per feeding treatment, underwent two digestibility trials. Exposure to 16L:8D photoperiod or a change from 16L:8D to 10L:14D increased similarly weight gain by 6.6% and feed intake by 9.5% without affecting feed efficiency. Calves fed WM consumed less feed (P < 0.05), had similar average daily gain (ADG) and were 25% more efficient than calves fed WB but calves fed RB had a lower average daily feed intake (P < 0.05), had similar ADG and were 10% more efficient than WB-fed calves. Calves fed RB had a tendency to have higher (P = 0.07) carcass weight and dressing percentage (118.8 kg and 53.6%, respectively) than calves fed WB (115.4 kg and 52.0%, respectively). Body and meat composition, meat color, and haematocrit and haemoglobin levels were not significantly affected by feeding or photoperiod treatments. Digestibility of dry matter (DM), energy (E), nitrogen, starch (S), phosphorus (P) and copper (Cu) were higher (P < 0.05) for calves fed WM compared to those fed WB. Furthermore, digestibility of DM, E, S, P and Cu were reduced (P < 0.05) in the diet containing WB compared to the diet containing RB. Diet did not affect energy intake even though, when expressed as a percentage of energy intake, calves fed WM retained more E (P < 0.05) than those fed WB (77.2 vs 64.7%) and calves fed RB had a higher E retention (69.8%) than those fed WB. Nitrogen intake and excretion were higher (P < 0.05) for the calves fed WB compared to those fed WM; there was no significant difference between both barley diets. Nitrogen retention was not affected by the diets. Blood urea level of calves fed WB was also 28.8% higher than blood urea level of calves fed WM. There was no significant effect of photoperiod treatments on diet digestibility, E and N retentions, and blood urea levels nor was there any significant interaction with diet treatments except on body weight changes. In conclusion, our results indicated positive effects of long-day photoperiod on growth performance but also showed evidence of photorefractoriness to subsequent photoperiod exposure. There was no effect of photoperiod on feed digestibility and feed efficiency. Digestibility and energy retention were lower with whole barley as compared with whole maize diet but were improved by rolling barley thus improving feed efficiency.

Crossbreeding parameters (line additive, dominance and additive × additive epistatic effects for individual and for maternal performance) on growth traits of females from a crossbreeding experiment between Holstein-based (HS) and Ayrshire-based (AS) lines were estimated by individual animal models, incorporating all known additive genetic relationships among animals, through restricted maximum likelihood and mixed-model methodologies. The growth traits [asymptotic weight (A), rate parameter (k), inflection parameter (m), average lifetime absolute growth rate (AGR), average lifetime absolute maturing rate (AMR) and average lifetime relative growth rate (RGR)] were estimated by fitting the Richards function to the observed growth curve of 3076 individuals. The statistical model included the random effect of the animal breeding value and the fixed effects of genetic group and station–year–season of birth. Results indicated that the HS exceeded (P < 0.001) the AS in additive effects for individual performance for both A and AGR. The HS exceeded (P < 0.05) the AS in additive effects for maternal performance for A. Individual heterosis was positive for A (P < 0.001) and for AGR (P < 0.01). Maternal heterosis was negative for A (P < 0.05) and positive for AMR (P < 0.05). Total heterosis (TH) had positive effects on both AGR and AMR (P < 0.05). Heterosis retained in advanced crossbred generations was not significant (P > 0.05) for any of the studied traits. The results suggest that crossbreeding designed to exploit TH can alter the shape of the growth curve of dairy cattle. Key words: Crossbreeding, dairy cattle, growth curve

The objective of this study was to compare the efficiency of cloprostenol and fenprostalene in synchronizing estrus. Before treatment, estrus was detected during 4.5 d for multiparous cows in exp. 1 (n = 105) and 7.5 d for primiparous and nulliparous females in exp. 2 (n = 86). Females that were not in estrus (exp. 1: n = 74 and exp. 2: n = 58) received at random, either 500 μg of cloprostenol (i.m.) or 1 mg of fenprostalene (s.c). Cattle synchronized with cloprostenol or fenprostalene that presented estrus within 5 d showed similar fertility rates (exp. 1: 86.1% vs. 88.0% and exp. 2: 89.3% vs. 72.2% for cloprostenol and fenprostalene, respectively) and PGF2α-estrus intervals (exp. 1: 68 h vs. 73 h and exp. 2: 57 h vs. 57 h). However, the incidence of synchronization (exp. 1: 97.3% vs. 67.6%, P < 0.001; and exp. 2: 93.3% vs. 64.3%, P < 0.01) and pregnancy rates (exp. 1: 83.8% vs. 59.5%, P < 0.05; and exp. 2: 83.3% vs. 46.4%, P < 0.01) were statistically higher for cloprostenol than for fenprostalene. In exp. 2, primiparous cows and heifers obtained similar reproductive performances. The fertility rate of cattle treated with cloprostenol in exp. 2 was higher than that of untreated cattle (89.3% vs. 50.0%, P < 0.001, n = 56). In exp. 1, the variance of interval to estrus was similar for both analogues, but in exp. 2, it was less variable after the administration of cloprostenol (P < 0.05). Intervals between cloprostenol injection and estrus (0–10 and 0–15 d) were shorter (P < 0.05) and less variable (P < 0.001) than fenprostalene–estrus intervals. These results indicate that cloprostenol has a better potential for estrus synchronization than fenprostalene. Key words: Cloprostenol, fenprostalene, estrus synchronization, prostaglandin F2α, beef cattle

Additive and nonadditive genetic ef- fects 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 Hol- stein pureline was superior to the Ayrshre-based pureline for direct addi- tive genetic merit for all traits. Heterosis

The effects of dietary hay or silage on plasma alpha-tocopherol and Se concentrations during late gestation and early lactation were studied using 40 crossbred pregnant cows and their calves. Cows received solely either timothy hay or grass silage forage from midgestation to early lactation and 21 d prior to estimated calving were or were not injected with Se (30 mg) and alpha-tocopherol (3000 IU). Five blood samples were collected for determination of concentrations of alpha-tocopherol and Se twice during late gestation and three times after calving. Blood samples from calves were collected at birth and at 10 and 30 d of age. Serum concentrations of alpha-tocopherol were low at birth for both groups of calves and ranged from .83 to 1.08 micrograms/ml of plasma. Hay had less alpha-tocopherol than silage (15 vs. 35 ppm in the DM). Cows fed silage had significantly higher plasma alpha-tocopherol concentrations (3.41 micrograms/ml) than cows fed hay (2.25 micrograms/ml). Cows given one subcutaneous injection of Se plus alpha-tocopherol preparation had significantly higher Se concentration in plasma (30 ng/ml) than did cows in the control group (17 ng/ml). The Se concentration in the placenta of cows that were injected with the Se preparation was significantly higher (64 ppm) than that in the control (47 ppm). Plasma Se concentration of calves at birth was correlated significantly with that of dams soon after parturition.

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.

We have isolated a bovine prolactin (bPRL) receptor cDNA from an endometrial cDNA library, which predicts a 557 amino acid transmembrane protein similar to the long forms of other characterized prolactin receptors. The predicted cytoplasmic domain is slightly truncated primarily by a stop codon located 36 codons 5' from the stop utilized in the human hepatic transcript. When expressed in COS cells, this cDNA was shown to encode a protein which bound bovine placental lactogen (bPL) and bPRL with nearly equal affinity (KD for bPL, 2.03 × 10−10 M; bPRL, 3.07 × 10−10 M). Northern analysis demonstrated multiple transcripts, with maternal liver, corpus luteum, intestine, endometrium and fetal liver containing a major transcript of about 3.8 kb, and maternal corpus luteum and endometrium, a second sized transcript of apparently equal abundance of 4.4 kb. This difference did not appear to be within the coding region. Primer extension analysis of maternal hepatic and endometrial transcripts revealed considerable heterogeneity. Examination of the distribution of prolactin and growth hormone receptor transcripts at mid-pregnancy by semi-quantitative reverse transcriptase polymerase chain reaction showed that both are widespread in bovine fetal and placental tissues. This isolation of bovine prolactin receptor cDNA, and description of receptor distribution will facilitate study of the action of the placental and pituitary members of this gene family during pregnancy.

Purebred Ayrshire females were assigned to two groups based on the breed of fetus carried during gestation. In group 1, Limousin embryos were transferred nonsurgically into Ayrshire recipients (10 heifers and 1 cow), and in group 2, 11 Ayrshire heifers and 1 cow were inseminated artificially to Ayrshire bulls. Blood samples were collected daily from d 265 of gestation until d 15 postpartum from 5 heifers of each group. Milk yield was recorded on alternate weeks during the first 20 wk postpartum. Calf birth weight was higher (44.2 vs. 35.4 kg) and gestation was longer (297.4 vs. 280.2) in Ayrshire dams bearing Limousin fetuses than in those bearing Ayrshire fetuses. Daily milk production for the first 20 wk was lower (18.1 vs. 20.8 kg) in Ayrshire dams bearing Limousin fetuses than in those bearing Ayrshire fetuses. Prepartum decrease in progesterone concentrations and increase in estrone concentrations were faster in Ayrshire heifers bearing Limousin fetuses than in those bearing Ayrshire fetuses. Profiles of peripartum concentrations of bovine placental lactogen differed between Ayrshire carrying different families of Limousin fetuses but were similar in those carrying families of Ayrshire fetuses. The concentrations of 15-keto-13,14-dihydroprostaglandin F2 alpha were lower during the postpartum period in heifers than gave birth to Limousin calves than in those that had Ayrshire calves. In conclusion, the breed of fetus influences physiological and endocrine responses of the dam, which might have some effect on milk production of the dam.

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.

Over 70% of homeless adults smoke cigarettes. Despite the desire to quit, this group rarely receives the external support to make or maintain a successful quit attempt (SQA; intentional quit attempt lasting >24 h). The Heaviness of Smoking Index (HSI) is a cigarette dependence measure that independently predicts SQAs among domiciled adults. For homeless adults, social support may be a way to buffer the impact of cigarette dependence on SQAs.The association of the HSI and past-year SQAs, and the potential moderating role of social support, was examined among 445 homeless smokers (Mage = 43.2 + 11.8, 65% male, 57.5% white). Support was measured by the International Support Evaluation List (ISEL-12) and its 3 subscales: tangible, belonging, & appraisal support.The HSI was negatively correlated with SQAs (r=−.283, p < .01) and in a regression model controlling for age, sex, and race/ethnicity, appraisal support significantly moderated this relationship (p < .05). The HSI was significantly related to SQAs across low, moderate, and high levels of appraisal support [mean, +1 SD; low (β=−.657, p < .001), medium (β=−.457, p < .001), and high (β=−.258, p < .05)]. Neither the ISEL-12 total nor the other subscales were moderators.The perceived availability of someone to talk to about one's problems appeared to attenuate the strength of the inverse relationship between the heaviness of smoking and SQAs. Fostering appraisal support for homeless smokers through group treatment may reduce the impact of cigarette dependence on making quit attempts. Social support coupled with the increased availability of empirically-supported cessation aids may improve dismal quit rates among homeless adults.