Two experiments were conducted to evaluate dry matter intake (DMI), milk yield, and milk composition from feeding rations that contained different sources of genetically modified whole cottonseed to Argentinean Holstein dairy cows. Twenty-four lactating multiparous Argentinean Holstein dairy cows were used in 2 experiments with a replicated 4 x 4 Latin square design, with cows averaging 565 kg body weight and 53 d in milk at the beginning of the experiments. Treatments in Experiment 1 were: Bollgard cotton containing the cry1Ac gene, Bollgard II cotton containing cry1Ac and cry2Ab genes, Roundup Ready cotton containing the cp4 epsps gene, and a control nongenetically modified but genetically similar cottonseed. In Experiment 2, two commercial sources, a parental control line, and the transgenic cotton containing both cry1Ac and cp4 epsps genes were used as treatments. All cows received the same total mixed ration but with different whole cottonseed sources. Cottonseed was included to provide 2.50 kg per cow daily (dry matter [DM] basis) or about 10% of the total diet DM. The ingredient composition of the total mixed ration was 32% alfalfa hay, 28% corn silage, 22% corn grain, 17% soybean meal, and 2% minerals and vitamins. In addition, genomic DNA was extracted from a subset of milk samples and analyzed by polymerase chain reaction followed by Southern blot hybridization for small fragments of the cry1Ac transgene and an endogenous cotton gene, acp1. No sample was positive for transgenic or plant DNA fragments at the limits of detection for the assays following detailed data evaluation criteria. The DMI, milk yield, milk composition, body weight, and body condition score did not differ among treatments. Cottonseed from genetically modified varieties used in these studies yielded similar performance in lactating dairy cows when compared to non-transgenic control and reference cottonseed.

The horn fly Haematobia irritans L. (Diptera: Muscidae) has recently spread to Argentina and Uruguay and is believed to cause damage to cattle hides. Four groups of ten Holstein steers each were maintained for 58 weeks under different infestation levels with H. irritans to determine if it was the cause of this problem. Hides (chrome tanned) from steers maintained under minimum infestation level had 4.7 +/- 3.8% of the area damaged. Maintaining the steers under low H. irritans level for the last 44 days of the trial using insecticidal ear-tags, resulted in 29.5 +/- 15.8% of hide area being damaged. Steers that were treated with 5% cypermethrin pour-on, when the H. irritans population was close to 50 flies, showed that 31.3 +/- 16.6% of hide area was injured, and 46.6 +/- 12.8% of damaged hide area was found in hides from non-treated steers. Significant differences were found between mean hide damage from steers maintained continuously under low H. irritans infestation levels and all other groups. Hyperaemia was significantly lower in the skin of steers under low H. irritans infestation level than in the skins of non-treated steers and steers maintained under low-level infestations for the final 44 days. Eosinophil and mononuclear cell infiltration was significantly lower when the population of H. irritans was less than six per steer than when the population was more than 100 flies per steer. Low numbers of Stomoxys calcitrans were found in all groups, but most hide damage was presumed due to H. irritans.

Ear tags containing 40% organophosphate insecticides (diazinon or diazinon plus chlorpyrifos-ethyl) were applied to control Haematobia irritans (L.) (Diptera: Muscidae) in treated (TG01 and TG02) and untreated (UG01 and UG02) groups of Holstein heifers born in 2001 and 2002, respectively. Control and treated groups were assessed for the abundance of Stomoxys calcitrans (L.) (Diptera: Muscidae) from August 2001 to April 2002 and again from August 2002 to April 2003. The treatment had a high efficacy for control of horn flies (maximum median number per heifer of TG01 and TG02 = 5) but a low effect on the abundance of stable flies. The total numbers of S. calcitrans were 1251 (42.9% of the total) and 1668 (57.1%) for TG01 and UG01, and 1423 (48.8%) and 1494 (51.2%) in TG02 and UG02, respectively. No significant difference in stable fly burden was found in 55 of the 76 weeks evaluated. A unimodal peak of abundance in the spring was found during the first fly season, and a bimodal abundance, with peaks in the spring and autumn, during the second season. No strong associations between horn fly and stable fly burdens was found in individuals of the CG01 (correlation coefficient = 0.13, P > 0.05) or CG02 (correlation coefficient = 0.538, P < 0.05, determination coefficient = 0.289).

Summary :The seasonal distribution of Haematobia irritans (Linnaeus, 1758) was evaluated at 31° 1 2' S -61° 29' W, Santa Fe, Argentina from November 1 992 to August 2000 by weekly fly counts on 20 Holstein cows not treated against ectoparasites. The analysis was mainly focused on winter fly abundance. Two peaks of abundance were found from spring to autumn. Adults of H. irritans were consistently found on cattle during winter, with increasing numbers from the end of July to late August. The only climatic parameter soundly correlated with the four week period, before each winter fly count, was the mean air temperature with the exception of year 1998. No significant relationship was found between level of cow infestation and relative humidity, saturation deficit and rainfall. Horn fly infestation on cows was lower than 20 % from end of June to end of August only in 1995, when mean air temperature was consistently lower than 1 ° C during the four week period previous to most fly counts. Conversely, the mean temperature was higher than 1 2° C previous to fly counts in 1998, when most cows remained infested. The results indicate that a proportion (unknown) of immature stages of H. irritans were insensitive to diapause inducing factors and developed through winter.

The effects of soybean by-products -soybean hulls (SH), soybean meal (SM) and raw soybean seeds (RSS) -on the rumen microbial population and fermentation were studied. The concentration of total rumen bacteria was greater (P = 0.06) for the SH and SM diets as compared to RSS. The concentration of cellulolytic bacteria tended to be higher with the SH and SM diets. Protozoal concentrations were significantly lower for the SH diet at feeding (T0, P < 0.05). Generic composition of protozoa was distinctly different among the soybean by-products. The composition of protozoa at T0 and 3 h (T3) for the SH diet group primarily consisted of vestibuliferids and Entodinium sp. with only 1% of protozoa from different genera present in the 6 h (T6) samples. The protozoa composition was more diverse with the SM and RSS diets, in that the "Others" types of entodiniomorphs included the genera Epidinium, Ophryoscolex, Metadinium, and Diplodinium. With the SH treatment, total VFA was greater and ruminal pH and acetate:propionate ratio were lower compared with the SM and RSS diets. Supplementation with all the soybean by-products modified both the microbial population and fermentation products and had an increased total dry matter intake in grazing dairy cattle.