No abstract

Under culture conditions, sex ratios in the European sea bass (Dicentrarchus labrax L.) are consistently skewed in favor of males. Moreover, no heteromorphic sex chromosomes have been shown for this species. This bias towards males could be due to a possible effect of environmental factors on sex differentiation, as has already been described in other fish species. To test this hypothesis, sexually undifferentiated sea bass were reared under two different thermal regimes or two different photoperiodic regimes, resulting in four groups: Group SP = short photoperiod (9 hours light [L]:15 hours dark [D]), Group LP = long photoperiod (15 L:9 D), both reared under natural temperature (24°C, average); Group LT = low temperature (15°C), Group HT = high temperature (25°C), both reared under natural photoperiod (13.5 L:10.75 D, average). Treatments lasted 80 days, from 57 to 137 days post fertilization, coinciding with the time when gonads are more sensitive to the action of exogenous sex steroids. The resulting sex proportions were determined by periodic histological examinations of the gonads during the first 2 years of age. No females were found in group LT at any sampling, whereas in the other groups, female proportions never reached values higher than 27%. Moreover, sex differentiation in group LT was delayed with respect to the other groups, as no fish completed sex differentiation until 16.4 months of age, compared to the other groups in which some individuals completed sex differentiation at 9 months of age. In addition, growth was significantly (P > 0.05) delayed in group LT with respect to the other three experimental groups and especially marked during the first year of life. Furthermore, the low values for the gonadosomatic index (GSI), together with the decrease of the number of spermatogenic males, denote a delay in gonadal maturation with respect to the rest of the experimental groups. The results of this study suggest that temperature can play an important role in the process of sex differentiation and growth of the sea bass. However, the mechanism(s) underlying this sexual lability remain unknown. J. Exp. Zool. 281:207–216, 1998. © 1998 Wiley‐Liss, Inc.

No abstract

Certified-organic dairy cows (n = 268) were used to evaluate the effect of 2 winter (December to April) housing systems on milk production, somatic cell score (SCS), body weight, body condition score (BCS), and economics across 3 winter seasons (2013, 2014, and 2015). Bedding cultures from the housing systems were also evaluated. Cows were randomly assigned to 2 treatments (2 replicates per group): (1) outdoor (straw pack, n = 140) or (2) indoor (3-sided compost bedded pack barn, n = 128). Cows calved during 2 seasons (spring or fall) at the University of Minnesota West Central Research and Outreach Center, Morris, Minnesota, organic dairy. Milk, fat, and protein production and SCS were recorded from monthly milk recording. Body weight and BCS were recorded biweekly as cows exited the milking parlor. Bedding cultures from the housing systems were collected biweekly. Costs for key inputs and the price received for milk production were recorded for the study period and averaged for use in the profitability analysis. Energy-corrected milk and SCS were not different for the outdoor (15.1 kg/d, 2.64) and indoor (15.7 kg/d, 2.57) housing systems, respectively. In addition, cows in the outdoor and indoor housing systems were not different for body weight (528 vs. 534 kg) and BCS (3.22 vs. 3.23), respectively. Daily dry matter intake was 19.1 kg/d for the outdoor cows and 19.6 kg/d for indoor cows. The total bacteria count from bedding samples tended to be lower in the outdoor (13.0 log 10 cfu/mL) compared with the indoor (14.9 log 10 cfu/mL) system. Milk revenue and feed cost were not different for the 2 housing systems. Labor and bedding costs were lower and net return was higher for the outdoor housing system. The outdoor straw pack system had a $1.42/cow per day net return advantage over the indoor compost bedded pack barn. In sum-mary, lactating cows housed outdoors on straw-bedded packs did not differ for production or SCS, or for body weight, BCS, or dry matter intake, but had greater profitability than cows housed in an indoor compost bedded pack barn.