Milk production and somatic cell counts: A cow-level analysis

Abstract

The objectives of this study were to quantify the relationship between 24-h milk loss and lactation milk loss due to mastitis at the cow level. For the year 2009, individual cow test-day production records from 2,835 Ontario dairy herds were examined. Each record consisted of 24-h milk and component yields, stage of lactation (days in milk, DIM), somatic cell count (SCC, ×10(3) cells/mL) and parity. The modeling was completed in 2 stages. In stage 1, for each animal in the study, the estimated slope from a linear regression of 24-h milk yield (kg), adjusted for DIM, the quadratic effect of DIM, and the 24-h fat yield (kg) on ln(SCC) was determined. In stage 2, the estimated slope were modeled using a mixed model with a random component due to herd. The fixed effects included season (warm: May to September, cool: October to April), milk quartile class [MQ, determined by the rank of the 24-h average milk yield (kg) over a lactation within the herd] and parity. The estimated slopes from the mixed model analysis were used to estimate 24-h milk loss (kg) by comparing to a referent healthy animal with an SCC value of 100 (×10(3) cells/mL) or less. Lactation milk loss (kg) was then estimated by using estimated 24-h milk loss within lactation by means of a test-day interval method. Lactation average milk loss (kg) and SCC were also estimated. Lastly, lactation milk loss (kg) was modeled on the log scale using a mixed model, which included the random effect of herd and fixed effects, parity, and the linear and quadratic effect of the number of 24-h test days within a lactation where SCC exceeded 100 (×10(3) cells/mL; S100). The effect of SCC was significant with respect to 24-h milk loss (kg), increasing across parity and MQ. In general, first-parity animals in the first MQ (lower milk yield animals) were estimated to have 45% less milk loss than later parity animals. Milk losses were estimated to be 33% less for animals in first parity and MQ 2 through 4 than later parity animals in comparable MQ. Therefore, the relative level of milk production was found to be a significant risk factor for milk loss due to mastitis. For animals with 24-h SCC, values of 200 (×10(3) cells/mL), 24-h milk loss ranged from 0.35 to 1.09 kg; with 24-h SCC values of 2,000 (×10(3) cells/mL), milk loss ranged from 1.49 to 4.70 kg. Lactation milk loss (kg) increased significantly as lactation average SCC increased, ranging from 165 to 919 kg. The linear and quadratic effect of S100 was a significant risk factor for lactation milk loss (kg), where greatest losses occurred in lactations with 5 or more 24-h test days where SCC exceeded 100 (×10(3) cells/mL).

Mediation analysis to estimate direct and indirect milk losses due to clinical mastitis in dairy cattle

“…Furthermore, in a recent field study, daily milk losses associated with SCC were higher than those associated with bacterial colony forming units (CFU); therefore, it was suggested that selection for increased resistance to mastitis (by increasing the number of SCC per bacterial CFU) would lead to cows not tolerant when infected (Detilleux et al, 2013). In other studies, the estimated impact of high SCC on production was a reduction of 0.7-3.7 kg milk per day in cows with clinical mastitis and SCC of 500,000 cells/mL (Hagnestam-Nielsen et al, 2009), which exceeded the 0.3-1.1 kg reduction in milk production in Holstein-Friesian cows with SCC of 200,000 cells/mL, i.e., in cows presumably free from clinical mastitis (Hand et al, 2012).…”

Estimativa das perdas de produção leiteira em vacas mestiças Holandês x Zebu com mastite subclínica baseada em duas metodologias de análise

“…Não houve diferença na produção de leite (P>0,05) entre vacas multíparas com e sem MSC. Os resultados encontrados neste trabalho para a metodologia convencional não eram esperados, uma vez que maiores perdas são esperadas em multíparas que em primíparas, devido às exposições prévias e consequentemente aos danos permanentes na glândula mamária (Hand, 2012). A magnitude das perdas encontradas foi diferente das observadas por Raubertas e Shook (1982), em que as primíparas perderam em média 135kg de leite na lactação, e as multíparas 270kg utilizando-se a mesma metodologia.…”

“…Nessa metodologia, a perda na produção foi expressiva e maior na fase final da lactação, sendo a produção das multíparas com MSC significativamente mais comprometida que das primíparas com MSC. Maiores perdas de produção por MSC são geralmente descritas em vacas multíparas do que em primíparas (Reneau, 1986;Hand, 2012). Segundo Bartlett et al (1990), pior saúde do úbere é mais esperada em multíparas que em primíparas e, no final da lactação, em ambas as categorias.…”

“…A MSC não apresenta sinais clínicos aparentes e ocorre com maior prevalência do que a mastite clínica em rebanhos leiteiros (Harmon, 1994;Gianneechini et al, 2002;Cunha et al, 2008), sendo classificada como de longa duração, quando majoritariamente provocada por patógenos contagiosos, ou de curta duração, causada principalmente por microrganismos ambientais (Chaneton et al, 2008). Perdas na produção de leite decorrentes do processo inflamatório que lesiona o parênquima mamário acontecem independentemente do microrganismo presente na glândula mamária (Hand, 2012;Harmon, 1994).…”

A new somatic cell count index to more accurately predict milk yield losses

“…The threshold for a healthy udder was considered to be an SCC of ≤ 50 000 (Seegers et al, 2003) or approximately 70 000 (Djabri et al, 2002;Schukken et al, 2003). Some authors defined a healthy animal as having a slightly higher SCC, i.e., ≤ 100 000 (Hand et al, 2012). Cows with an SCC of less than 100 000 are considered to be non-infected, with no significant milk yield losses owing to subclinical…”