Records representing 19,266 Holstein cows from Arizona DHIA data over a 5-yr period were analyzed to determine the effects of season and lactation number on milk production and reproduction. Seasons were winter (December, January, and February), spring (March, April, and May), summer (June, July, and August), and fall (September, October, and November). Traits analyzed by least squares ANOVA were 305-d FCM, complete lactation milk, calving interval, and services per conception. All sources of variation were significant except the interaction between lactation number and season of calving for complete lactation milk. Milk production was depressed for cows calving in summer and fall. First lactation cows had lowest milk production, and highest production occurred in either lactation 4 or 5. Cows calving in spring and summer had reduced reproductive performance, as measured by calving interval and services per conception. First lactation cows had lowest values for both reproductive traits. Previous days dry was negatively related to milk production for spring calvings but was positively related for all other seasons. Cows with higher milk production had reduced reproductive performance. Partial regression coefficients for calving interval and services per conception were 12 d and .25 services per conception per 1000 kg of 305-d FCM, respectively. Despite the negative effects of thermal stress, milk production and fertility in this study were not depressed as severely as in previous research reported from Arizona. Calving schedules may be adjusted to minimize the adverse effect of heat stress.

The specific purpose was to investigate the possible interrelationships of genotypes of Staphylococcus aureus found in mammary glands, horn flies, and extramammary sites on 3 southeastern US dairies. A total of 1,228 samples were obtained from various sources on the 3 dairy herds, each of which had a history of Staph. aureus mastitis. Dairy herds studied had access to pasture, and samples were collected during the summer when horn flies (Haematobia irritans) were active. Samples collected included milk samples from all lactating herd cows, colostrum samples from heifers calving during the study period, heifer body sites (mouth, nostrils, and teats), the heifer environment (water, feed, and soil/vegetation/pasture), horn flies, and humans (hands and nostrils). Isolation of Staph. aureus was attempted from all samples, with isolates subjected to genotypic analysis using pulsed-field gel electrophoresis. A total of 244/1228 (or 19.9%) of all samples were positive for Staph. aureus. For milk samples, 52/383 (or 13.6%) of samples were Staph. aureus positive, and 70/411 (or 17.0%) of heifer quarter colostrum samples were positive. Horn fly samples were frequently positive, with over one-half (29/52, or 55.8%) of samples positive for Staph. aureus. Staphylococcus aureus obtained during the study comprised isolates from 12 different genotype groups as defined in this study. Identical genotypes were obtained from horn flies, heifer colostrum samples, and cow milk samples. Group B genotypes were shared among flies, heifer colostrum samples, body sites, and cow milk samples, whereas group A genotypes were common to the same sample locations and body sites but rarely (once) found in horn flies. We conclude, based upon the finding of identical pulsed-field gel electrophoresis genotypes in flies, heifer body sites, and heifer colostrum samples, that flies and heifer body sites could be important sources of Staph. aureus for heifer intramammary infections.

Two trials were conducted with 24 primiparous suckled beef heifers to determine independent and combined effects of a prolactin-suppressing agent and exogenous steroids on serum hormones and reproductive activity. Heifers were assigned in groups of six to one of four treatments: 1. (C)-subcutaneous control injections administered once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpartum or until first naturally occurring estrus; 2. (CB)-subcutaneous injections of 80 mg CB-154 (2-bromo-~-ergokryptine) (Sandoz) in ethanol once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpartum or until first naturally occurring estrus; 3. (PE)-intramuscular (IM) injection of 25 mg progesterone in sesame oil on day 15 postpartum, followed by IM injection of 4 mg estradiol-17 in sesame oil 48 hr later, or 4. (CBPE)-treatments 2 (CB) plus 3 (PE). A marked reduction in serum prolactin was observed after a single injection CB-154 in all CB and CBPE treated heifers, reaching minimum concentrations by day 7 postpartum after a second injection on day 6. Continued treatment decreased (P<.01) prolactin concentrations over the 35 day blood sampling period to an average of .9 + .2 ng/ml as compared to 19.2 + 5.6 ng/ml for non-CB-154 treated (C and PE) heifers. In non-CB-154treated heifers, serum prolactin was higher during the spring (33.5 -+ .9 ng/ml) than the fall (2.6 + .9 ng/ml). Treatment CB had no effect on serum concentrations of LH, estradiol-17/3 or progesterone. The resumption of cyclic activity in C and CB heifers prior to day 40 postpartum was characterized in four of six animals by 4-to 5-day elevations of serum progesterone and 7-to 8-day cycles, which were preceded in every case by peaks of estradiol-17/3 (9 + 1.9 pg/ml) and nonstanding estrous behavior (three of four) or no behavior (one of four). Palpable corpora lutea were detected in two of four animals during these progesterone increases. Subnormal luteal function was followed by another estradiol-i7/3 peak (7 ---2 pg/ml) and estrus (three of four) or nonstanding estrus (one of four). Injection of progesterone followed by injection of estradiol-17/3 resulted in a preovulatory discharge of LH in 12 of 12 PE and CBPE heifers, with eight of 12 initiating luteal function within 72 hr after the LH surge. On the basis of endocrine data, suppression of endogenous prolactin release did not (P<.05) potentiate steroid treatment effects. Treatments PE and CBPE resulted in a reproductive trend which reflected endocrine findings. Data fail to provide evidence that prolactin is antigonadotropic in bovine heifers. (

No abstract

Thirty-seven Holstein and 26 Brown Swiss dairy cows were used to evaluate the effect of two different cooling systems on physiological and hormonal responses during the summer. A control group of cows had access only to shade (C). A second group was cooled with spray and fans (S/F) and the third group was under an evaporative cooling system called Korral Kool (KK). The maximum temperature humidity index during the trial was from 73 to 85. Rectal temperatures and respiration rates of the C group were higher (P<0.05) than those of the S/F and KK groups in both Holstein and Brown Swiss cows. Triiodothyronine levels in milk were higher (P<0.05) in the KK group than in the S/F and C groups, while cortisol levels were lower (P<0.05) in the C group than in S/F and KK. There was no significant difference in the hormonal response of the two breeds. These results demonstrate that both cooling systems may be used increase the comfort of Holstein and Brown Swiss cows during summer in hot, dry climates.

Calving difficulty at first and second parturition, using data recorded on 476 purebred Charolais heifers from a ranch in Southeastern Arizona, were analyzed by analysis of variance, step-wise multiple regression and discriminant analysis. Dystocia score (1 = no assistance through 4 = extreme difficulty) was the dependent variable with dam and calf effects independent variables. In this herd, 31.1 and 15.0% of the heifers experienced calving difficulty at first and second parturition, respectively. Birth weight of calf was the most important factor influencing dystocia, accounting for 71 and 61% of the total variation explained by the analysis of variance model when calf effects as well as dam effects were included at first and second parturition. Mean birth weight was 39.0 kg for primiparous heifers and 44.3 kg for second-half cows. A significant increase in dystocia (at both first and second parturition) occurred among male calves with birth weights of 45.5 kg or greater. At first parturition, no significant increase in dystocia occurred among female calves until birth weight exceeded 50 kg. Birth weight was not a significant factor influencing dystocia for female calves at second parturition. Yearling weight of cow and dystocia score of cow's dam were the only significant dam variables, and only at first parturition. Pelvic height measurements did not significantly affect dystocia scores at either parturition. A reasonably accurate prediction of dystocia based on the variables included in this study would be impossible, even if some means were devised to reliably predict birth weight of the calf.

No abstract

Four experiments involving 16 pens of 8 to 10 crossbred steer calves each were conducted at Yuma, Arizona. Initial and final weights were approximately 170 and 275 kg, respectively. The experimental design was a 2 x 2 x 4 factorial replicated over 2 yr with main effects for season (summer, winter), diet (H = ground alfalfa hay, H + G = 50% ground alfalfa, 47.5% dry-rolled wheat and 2.5% molasses) and water source (N = normal, S = saline) during two consecutive 56-d periods in each experiment (N-N, N-S, S-N, S-S). Normal water contained approximately 1,300 ppm, and saline water contained approximately 6,000 ppm, total dissolved salts. Steers on the H + G diet gained 32% faster (P less than .01) and consumed 4% less (P less than .01) feed than those on the H diet. Gain and feed intake during winter were greater than during summer (20% and 7%, respectively, P less than .01). Gain and feed intake were reduced approximately 9% (P less than .01) on S water combinations compared with N-N water. Depression in gain and feed intake due to heat stress (summer season) or S water ingestion was greater on the H diet (diet x water source and diet x season interactions, P less than .02). Although season x water source interactions were not significant, saline water ingestion tended to be more detrimental during periods of heat stress (summer). Apparent adaptation to saline water occurred on the H + G diet, but not on the H diet.(ABSTRACT TRUNCATED AT 250 WORDS)