Non-saleable milk (waste milk, WM) is contaminated with an undefined spectrum of potentially harmful pathogens and antimicrobial residues. The objective of this study was to determine the impact of feeding bulk milk (BM) or WM - both pasteurized or not - on calf performance, health and the antibiotic resistance of specific faecal bacteria. A total of 114 calves from a large-scale dairy were housed outdoors in individual hutches and were randomly assigned to one of four feeding groups. The calves were fed either WM, pasteurized WM (pWM), BM or pasteurized BM (pBM) from day 3 to 56 of life. Milk samples taken from the pasteurizer and calves' nipple buckets were investigated at regular intervals for total plate count and counts of thermoduric bacteria, coliforms and mastitis pathogens. Faecal samples were taken on days 2, 14, 28 and 56 of life from randomly selected calves of the WM, pWM and BM groups (each N = 8-9) and processed to obtain from each sample preferably two isolates of Escherichia (E.) coli and Enterococcus spp. respectively. Isolates were tested for their antimicrobial susceptibility to 25 antimicrobial agents by broth microdilution. Daily weight gain, milk and calf starter intake and health parameters did not differ significantly between the calves of the four feeding groups. The proportion of resistant E. coli isolates was significantly higher in calves fed WM and in calves fed pWM (most pronounced for cephalosporins) than in calves receiving BM. No differences in resistance were found for Enterococus spp. Thus, the concerns for selecting resistant faecal bacteria by feeding WM seem to be justified. Nonetheless, pasteurized WM of cows not treated with antimicrobials represents an acceptable feed for young calves.

The aim of this study was to evaluate the effects of dietary Quebracho tannin extract (QTE) on feed intake, apparent total tract digestibility (ATTD), excretion of urinary purine derivatives (PD) and milk composition and yield in dairy cows. Fifty Holstein cows were divided into two groups. To reach a similar performance of both groups, cows were divided according to their milk yield, body weight, days in milk and number of lactations at the start of the experiment averaging 33.2 ± 8.2 kg/d, 637 ± 58 kg, 114 ± 73 d and 2.3 ± 1.6 lactations, respectively. The cows were fed a basal diet as total mixed ration containing on dry matter (DM) basis 34% grass silage, 32% maize silage and 34% concentrate feeds. Three dietary treatments were tested, the control (CON, basal diet without QTE), QTE (basal diet with QTE at 15 g/kg DM) and QTE (basal diet with QTE at 30 g/kg DM). Two treatments were arranged along six periods each 21 d (13 d adaptation phase and 8 d sampling phase). The ATTD of DM and organic matter were reduced only in Diet QTE, whereas both QTE treatments reduced ATTD of fibre and nitrogen (N), indicating that QTE impaired rumen fermentation. Nevertheless, feed intake was unaffected by QTE. In Diet CON, urinary N excretion accounted for 29.8% of N intake and decreased in treatments QTE and QTE to 27.5% and 17.9%, respectively. Daily faecal N excretion increased in treatments CON, QTE and QTE from 211 to 237 and 273 g/d, respectively, which amounted to 39.0%, 42.4% and 51.7% of the N intake, respectively. Hence, QTE shifted N excretion from urine to faeces, whereas the proportion of ingested N appearing in milk was not affected by QTE (average 30.7% of N intake). Daily PD excretion as indicator for microbial crude protein (CP) flow at the duodenum decreased in treatment QTE compared with Diet CON from 413 to 280 mmol/d. The ratios of total PD to creatinine suggest that urinary PD excretion was already lower when feeding Diet QTE. While there was no effect of Diet QTE, treatment QTE reduced milk yield, milk fat and protein. Both QTE treatments reduced milk urea concentration, which suggest that ruminal degradation of dietary CP was reduced. In summary, adding QTE at dosages of 15 and 30 g/kg DM to diets of lactating dairy cows to improve feed and protein use efficiency is not recommended.

The objectives of this study were to evaluate the effects of replacing maize silage plus soybean meal with red clover silage (RCS) plus wheat on feed intake, diet digestibility, N partitioning, urinary excretion of purine derivatives, and milk production in dairy cows. Forty-four lactating German Holstein cows were used in a 4 × 4 Latin square design with 21-d periods composed of a 13-d adaptation phase followed by an 8-d sampling phase. Experimental diets offered as total mixed ration consisted of a constant forage-to-concentrate ratio (75:25) with targeted proportions of RCS-to-maize silage of 15:60 (RCS), 30:45 (RCS), 45:30 (RCS), and 60:15 (RCS) on a dry matter (DM) basis. Increasing the proportion of RCS plus wheat in the diet decreased linearly the intake of DM from 22.4 to 19.8 kg/d, and of organic matter from 21.1 to 18.1 kg/d. The apparent total tract digestibility (ATTD) of DM and organic matter did not differ across diets and averaged 68.4 and 70.5%, respectively. However, ATTD of N decreased linearly from 68.5 to 63.2%, whereas ATTD of neutral detergent fiber and acid detergent fiber increased linearly from 50.4 to 59.6% and from 48.4 to 57.7%, respectively, when increasing the proportion of RCS plus wheat. Fecal N excretion increased from 31.6 (RCS) to 37.2% (RCS) of N intake, whereas urinary N excretion was the lowest (32.8% of N intake) with RCS. Hence, N efficiency (milk N/N intake) decreased linearly with incremental levels of RCS plus wheat, being the lowest when feeding RCS (25.4%), probably due to increased nonprotein N proportion in total dietary N. Urinary excretion of purine derivatives decreased linearly from 378 to 339 mmol/d, which suggests that increasing levels of RCS plus wheat reduced the microbial crude protein flow at the duodenum. Milk yield and milk protein concentration declined linearly from 35.9 to 30.2 kg/d and from 3.20 to 3.01%, respectively, when increasing the proportion of RCS plus wheat. In conclusion, caution should be taken before introducing high levels of RCS plus wheat in diets of high-yielding dairy cows. However, RCS plus wheat can be included up to 30% of the dairy cow diet (DM basis) without a reduction in lactation performance.

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