Daily rhythms in blood and milk lead toxicokinetics following intravenous administration of lead acetate to dairy cows in summer.

The objective of this study was to investigate circadian variations of blood and milk lead toxicokinetics in dairy cows in summer. Twenty lactating Holstein animals were randomly assigned to four treatments corresponding to different hours after onset of light (HALO): 2, 8, 14, and 20. Cows received a single intravenous administration of 2.5 mg/kg lead as lead acetate. Blood and milk samples were taken and analyzed by atomic absorption spectrophotometry. For each toxicokinetic parameter, a one-way analysis of variance (ANOVA) was performed to outline the existence of daily variations. Significant blood differences as a function of HALO were found for the hybrid constant of distribution (alpha), hybrid constant of elimination (beta), elimination half-life (t(1/2)beta), area under the curve (AUC), volume of distribution at steady state (V(ss)) and clearance (Cl(B)) (p<0.05). Half-life of elimination presented two peaks at 2 and 14 HALO. Milk data showed significant differences for maximum concentration and AUC (p<0.05). The ratio AUC(milk)/AUC(blood) was utilized to estimate penetration of lead in milk. It differed significantly throughout the day (p<0.05). Milk data for the significant parameters could be fitted to circadian rhythms. No circadian rhythms were detected in blood parameters or in the ratio AUC(milk)/AUC(blood).

Diet and cooling interactions on physiological responses of grazing dairy cows, milk production and composition.

The objective of this trial was to evaluate the effects of diet and cooling in the holding pen before milking on rectal temperature, respiration rate and milk production and composition. Fifty-eight lactating Holstein cows were used in a factorial split-plot design, at Rafaela Experimental Station from 12 January to 3 March 2003. The treatments were combinations of two diets: control (CD) and balanced (BD) with two levels of cooling before milking: none (NSF) and a sprinkler and fans (SF). Forage:concentrate ratios for CD and BD were 81:19 and 68:32, respectively. Cows were milked twice daily. Milk production was recorded daily, and milk composition (fat, protein, lactose and urea) was analysed twice a week. The physiological data were recorded once a week, before the cattle entered the holding pen and after milking, in the afternoon. Average maximum weekly temperature humidity index was 75.4 and ranged from 61.4 to 83. There were highly significant effects of cooling on physiological responses. Milk production was affected by diet and cooling, with no interaction; the highest and lowest production of milk was 22.42 and 20.07 l/cow per day, for BD+SF and CD+NSF, respectively. Protein was affected by diet, and was higher for BD (3.17 vs. 3.08%). There were interaction effects on milk fat at the 8% level, the highest concentration being 3.65% for BD+NFS. It was concluded that under grazing conditions, cooling by sprinkler and fans before milking improves the comfort of dairy cows, and that the effects on milk production and composition are enhanced when diets are specially formulated for heat-stress periods.

Hydrogenated fish fat for grazing dairy cows in summer.

Thirty-two multiparous Holando argentino cows in mid lactation were randomly assigned to two treatments: control or HFF (hydrogenated fish fat) at Rafaela, 31 degrees 11' South, during summer 1997/1998, to evaluate the effect of using HFF as a supplement under grazing conditions. Animals in both treatments grazed an alfalfa pasture, and were confined from 1000 hours to 1700 hours daily in a shaded pen where water was provided ad libitum. During each milking, animals in the control group received 3.73 kg dry matter per cow each day (DM cow(-1) day(-1)) concentrate (15% crude protein; 8.69 MJ energy for location/kg DM). Cows in the HFF group received 3.25 kg DM cow(-1) day(-1) concentrate, plus 0.200 kg DM cow(-1) day(-1) HFF. Both diets presented similar energy, protein and neutral detergent fibre contents. The trial was performed during a strong "El Niño" event, which resulted in a total rainfall of 396.3 mm (80% higher than normal). The mean temperature was 23.7 (SD 3.2) degrees C and the mean temperature humidity index was 72.9 (SD 4.96). Production data were analysed using a completely randomised design with analysis of covariance. Supplementation with HFF produced an increase in daily milk production (26.4 (SD 2.46) l/cow compared to 23.9 (SD 2.68) l/cow for the controls; P<0.05). Milk fat production was higher for HFF (P<0.05): 941 (SD 96) g cow(-1) day(-1) as compared to controls, which yielded 846 (SD 95) g cow(-1) day(-1). Milk protein yields also differed significantly (P<0.05), the respective values for HFF and controls being 795 (SD 72) g cow(-1) day(-1) and 715 (SD 83) g cow(-1) day(-1). It was concluded that hydrogenated fish fat could be a good ingredient to sustain high yields and elevated maintenance requirements in a grazing system during hot conditions.

Chronobiological variations of indomethacin pharmacokinetic parameters in sheep.

A two-phase study to investigate the influence of administration time on pharmacokinetics of indomethacin in sheep was performed. In phase I, 12 animals were allocated to four groups, each corresponding to a different time: 08:00, 14:00, 20:00, 02:00 h. Sheep received an intravenous administration of 1 mg/kg indomethacin. In phase II, each group was administered indomethacin with a 12-h difference compared to Phase I. The trial was performed in autumn, and animals were subjected to a natural light:dark cycle of 10:14 h. Blood samples were taken and processed by high performance liquid chromatography (HPLC) with ultraviolet detection. For each pharmacokinetic parameter, an analysis of variance was performed to outline the existence of chronobiological variations. Concentration at zero time (C0), hybrid constant for distribution and its half life, hybrid constant for elimination and its half-life, volume of distribution (V(d)), area under the curve (AUC(infinity)) and clearance rate (Cl), presented chronobiological variations (P < 0.05) and were fitted to a cosine equation. The following parameters adjusted to circadian rhythms: C(0) (acrophase: 13.9788 h); AUC(infinity) (acrophase: 13.4377 h); V(d) (acrophase: 0.8245 h) and Cl (acrophase: 1.4965 h). It was concluded that pharmacokinetic parameters of intravenously injected indomethacin in sheep would behave in a different, though predictable, manner according to the animal's biological clock.

Chronotoxicology of florfenicol.

Sixty 3-month-old homozygote male mice were studied for circadian rhythmicity in the toxicity of florfenicol overdose. Animals were kept under a regimen of 12h light, 12h darkness (12:12 LD) with food and water available ad libitum. The LD50 (median lethal) dose was determined in a preliminary experiment and was administered to groups of 10 mice at six different clock times (hours) after light onset (HALO): 0, 4, 8, 12, 16, and 20 HALO. Cosinor analysis verified a statistically significant (P < .04) circadian rhythm in the toxic effect (mortality) of florfenicol. Mortality was greatest when the drug was injected 4h after the commencement of the activity span (16 HALO) and least when injected 4h after the start of the diurnal rest span (4 HALO). Mortality was 2.5 times greater when drug injection was given at 16 HALO than at 4 HALO.

Evaluation of different shades to improve dairy cattle well-being in Argentina.

Two tree shades (TS1 and TS2) and an artificial shade structure (AS) were evaluated using black globe temperatures (BGTs) to assess their effectiveness in reducing heat load. The artificial structure consisted of a black woven polypropylene cloth providing 80% shade, mounted on 2.5-m-high eucalyptus posts. The work was carried out at Rafaela Experimental Station, Argentina, during the summer (January and February) 1994. BGTs and floor temperatures were measured in concrete floor holding pens with and without artificial shade. The results showed no difference between TS1, TS2 and AS, their average BGTs being 30.2 (SD 0.58), 29.0 (SD 0.70) and 30.2 (SD 0.74) degrees C, respectively. BGTs under all three shades were significantly lower (P < 0.01) than the average BGT recorded outside: 35.5 (SD 1.12) degrees C. Average BGTs in holding pens were 32.4 (SD 1.38) and 39.9 (SD 1.91) degrees C for shaded and non-shaded areas (P < 0.01). The corresponding average floor temperatures were 27.8 (SD 0.68) degrees C and 47.7 (SD 2.13) degrees C (P < 0.01). To assess the effects of shade on animal well-being, afternoon rectal temperatures (RT) and respiratory rate (respirations per minute, RR) of lactating cows were recorded twice a week. Rectal temperatures were significantly higher for non-shaded cows (P < 0.01), mean RT being 40.1 (SD 0.65) degrees C vs 39.3 (SD 0.42) degrees C for the shaded animals. Corresponding RRs were 78.9 (SD 18.0) and 60.7 (SD 10.6) (P < 0.05). It was concluded that: (1) tree and artificial shades produced similar effects, (2) shading the holding pen with an 80% shading cloth was effective in reducing heat load and floor temperatures, and (3) access to shade in our pasture-based system improved animal well-being.