Marcos André Arcari

Bovine subclinical intramammary infection caused by coagulase-negative staphylococci increases somatic cell count but has no effect on milk yield or composition

The aim of this study was to evaluate the effect of subclinical intramammary infection (IMI) caused by coagulase-negative staphylococci (CNS) as a group and by specific CNS species on milk yield and composition and somatic cell count (SCC) of dairy cows. Selection of cows with IMI caused by CNS was performed by microbiological cultures of composite samples collected from 1,242 dairy cows distributed in 21 dairy herds. After selection of cows, milk yield was measured and milk samples were collected at the mammary quarter level (i.e., 1,140 mammary samples collected from 285 cows) for analysis of milk composition and SCC. In total, 108 isolates of CNS were identified at the species level by PCR-RFLP analysis. Forty-one pairs of contralateral mammary quarters, with and without IMI, were used to evaluate the effect of CNS on milk yield and composition. Mammary quarters infected with CNS had higher geometric mean SCC (306,106 cells/mL) than noninfected contralateral mammary quarters (62,807 cells/mL). Intramammary infection caused by CNS had no effect on milk yield or on contents of fat, crude protein, casein, lactose, total solids, and solids-not-fat. Staphylococcus chromogenes was the most prevalent CNS species in this study and the only species that allowed within-cow evaluation. The IMI caused by S. chromogenes increased SCC but had no effect on milk yield and composition at the quarter level. In conclusion, subclinical mastitis caused by CNS increased the SCC but had no effect on milk yield and composition of dairy cows.

Effects of bovine subclinical mastitis caused by Corynebacterium spp. on somatic cell count, milk yield and composition by comparing contralateral quarters.

Subclinical mastitis caused by Corynebacterium spp. (as a group and at the species level) was investigated by evaluating contralateral (healthy and infected) mammary quarters for somatic cell count (SCC), milk yield and composition. Selection of cows with subclinical mastitis caused by Corynebacterium spp. was performed by microbiological culture of composite samples collected from 1242 dairy cows from 21 dairy herds. For each of the selected cows, milk yield was measured and milk samples were collected at the mammary quarter level (i.e., 1140 mammary samples collected from 285 cows) for analysis of milk composition and SCC. The identification of Corynebacterium spp. isolates was performed by 16S rRNA gene sequencing. One hundred and eighty Corynebacterium spp. isolates were identified, of which 167 (92.77%) were C.bovis and eight (4.44%) non-C.bovis; for five of the Corynebacterium spp. isolates (2.77%), sequencing of 16S rRNA genes did not allow identification at the species level. Mammary quarters infected with Corynebacterium spp. as a group had a higher geometric mean SCC (197,900 cells/mL) than healthy contralateral mammary quarters (85,800 cells/mL). Species of Corynebacterium non-C.bovis were infrequently isolated and did not change SCC, milk yield or milk solid contents when evaluated at the contralateral quarter level. Although C.bovis infection showed no effect on milk yield, fat, protein, casein or total solids in milk, it increased SCC and decreased lactose and milk solids non-fat content.

Effect of dietary cation-anion difference on ruminal metabolism, total apparent digestibility, blood and renal acid-base regulation in lactating dairy cows.

The present study aimed to evaluate the effect of dietary cation-anion difference (DCAD) on ruminal fermentation, total apparent digestibility, blood and renal metabolism of lactating dairy cows. Sixteen Holstein cows were distributed in four contemporary 4×4 Latin Square designs, which consisted of four periods of 21 days and four treatments according to DCAD: +290; +192; +98 and -71 milliequivalent (mEq)/kg dry matter (DM). Ruminal pH and concentrations of acetic and butyric acid increased linearly according to the increase of DCAD. Similarly, NDF total apparent digestibility linearly increased by 6.38% when DCAD increased from -71 to 290 mEq/kg DM [Y=65.90 (SE=2.37)+0.0167 (SE=0.0068)×DCAD (mEq/kg DM)]. Blood pH was also increased according to DCAD, which resulted in reduction of serum concentrations of Na, K and ionic calcium (iCa). To maintain the blood acid-base homeostasis, renal metabolism played an important role in controlling serum concentrations of Na and K, since the Na and K urinary excretion increased linearly by 89.69% and 46.06%, respectively, from -71 to 290 mEq/kg DM. Changes in acid-base balance of biological fluids may directly affect the mineral composition of milk, as milk concentrations of Na, K, iCa and chlorides were reduced according to blood pH increased. Thus, it can be concluded that the increase of DCAD raises the pH of ruminal fluid, NDF total apparent digestibility, and blood pH, and decreases the milk concentration of cationic minerals, as well as the efficiency of Na utilization to milk production.

Balanço de nitrogênio e composição do leite de vacas alimentadas com ureia e farelo de soja e dois teores de proteína em dietas com cana-de-açúcar

Braz. J. Vet. Res. Anim. Sci., São Paulo, v. 51, n. 3, p. 242-251, 2014 Abstract It was evaluated the effect of feeding two levels of crude protein (CP) (low: 142 g CP/kg DM; and high: 156 g CP/kg DM) and two nitrogen sources (soybean meal and urea) to dairy cows using sugar cane as forage on microbial protein synthesis, the composition of the milk nitrogen fraction, nitrogen (N) balance and blood parameters. Twelve Holstein cows with an average milk yield of 22.0 ± 2.3 kg/day, and with 235 ± 40 days in milk were included in this study. The animals were grouped into three balanced and contemporary 4x4 Latin squares for an experimental period of 21 days. On the 15th day of each period, milk and urine samples were collected for microbial protein synthesis determination. Total excretion of urine (L/day), milk urea nitrogen (MUN) and blood urea were higher for the diets with high CP, regardless of the nitrogen source. Nitrogen efficiency was higher for cows fed diets with low CP. Cows in the final third of lactation can be fed diets with reduced CP levels, regardless of the nitrogen source, soybean meal or urea, without influencing the synthesis of microbial protein or the composition of the nitrogen fraction of milk.

Letter to the editor: A response to the comments of Silanikove et al. (2015)

We very much appreciate the interest in our recent publication “Bovine subclinical intramammary infection caused by coagulase-negative staphylococci increases somatic cell count but has no effect on milk yield and composition” (Tomazi et al., 2015). In reference to the comments, Silanikove and colleagues (2015) first raised concerns about the implication of our results, which showed that at the quarter level, IMI caused by CNS increased the SCC of milk, but had no effect on milk composition and yield of dairy cows. In their comments, they expressed concern that “adoption of the implication of this study might be associated with dissemination of an erroneous concept regarding the importance of CNS infection...” Then, Silanikove et al. (2015) questioned our assumption that “no previous studies reported the effect of IMI caused by CNS on milk yield and composition by comparison of contralateral mammary quarters.” Three papers (Leitner et al., 2006, 2011; Silanikove et al., 2014b) were cited to support their contention and they declared that, based on these studies, IMI caused by CNS had a significant effect on milk composition; specifically, on casein and lactose concentrations. They also observed that IMI caused by CNS had a negative effect on “milk clotting parameters as reflected by lower curd firmness and increased rennet clotting time, consistent with similar findings in goats and sheep.” Silanikove et al. (2015) also indicate that “it should be noted that mixing bacterially contaminated milk with milk from noncontaminated glands negatively affects the clotting parameters of the uninfected milk” according to Silanikove et al. (2014a) and Leitner et al. (2008). In response to the first comment, and as described in our study, “the effect of IMI caused by CNS on milk yield and composition remains inconclusive.” Therefore, it would be no surprise to find studies reporting different trends in terms of the effect of IMI caused by CNS on milk yield and composition. The possible reasons for these differences in results were also described in our paper: “The variability among studies on the effect of CNS on milk yield and composition might be attributed to differences in study design and challenge conditions.” (Tomazi et al., 2015; page 3071) Our results are consistent with other studies (Kirk et al., 1996; Paradis et al., 2010; Pearson et al., 2013; Hertl et al., 2014; Silanikove et al., 2014b), which also reported no effect of IMI caused by CNS on milk yield in dairy cows. Effect of CNS IMI on milk production of dairy cows was not observed even when comparing monozygotic twins (Pearson et al., 2013). In addition, we should consider that some studies have reported higher milk production in cows with IMI caused by CNS relative to that of uninfected cows (Schukken et al., 2009; Piepers et al., 2010, 2013), which might be attributed to a protective effect of pre-existing CNS IMI against more-virulent mastitis pathogens. Thus, considering these recent published studies and the considerable number of contralateral mammary quarters evaluated in our study, we still consider that our conclusion that IMI caused by CNS did not alter milk yield and gross milk composition of dairy cows is correct and not an “erroneous concept.” In response to the second comment, according to Leitner et al. (2006), based on a limited number of bovine mammary quarters for evaluation of milk composition (11 mammary quarters infected by Staphylococcus chromogenes vs. 33 uninfected quarters), the results indicated no difference between infected and uninfected quarters relative to fat, protein, and lactose concentrations. It should be noted that, according to Leitner et al. (2006), lactose contents were statistically similar between uninfected (144 ± 3 mM) and infected quarters (140 ± 6 mM). Similar results on gross milk composition were also reported by Silanikove et al. (2014b). As described in Table 2 of Silanikove et al. (2014b), at the gland level, IMI caused by CNS had no effect of on fat, protein, or lactose contents when comparing uninfected and infected quarters. The lactose contents reported in the latter study were 50.2 ± 2.4 g/L for Letter to the editor: A response to the comments of Silanikove et al. (2015)