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Traditionally the lactation cycle of a dairy cow is based around a 12-month calving interval, allowing for 10 months of lactation, followed by a 2-month dry period. This means that the cow has to conceive within 2-3 months after calving, when she is also at peak lactation and metabolically is in a negative energy balance. Such challenging physiological conditions make it challenging for the cow to conceive at this time and many modern high-producing cows fail to get pregnant within the constraints of a 12-month calving interval. In addition, many cows still produce at a high level at drying-off time, increasing the risk of intramammary infections. Therefore, delaying conception past peak production and, as a result, extending the lactation beyond 10 months may increasingly be necessary. Additionally, extended lactation (EL) may offer other advantages such as fewer calves being born and thus fewer 'surplus' calves needing to be culled at a young age, fewer health and welfare issues and improved environmental outcomes (i.e. less greenhouse-gas emission; less antibiotic usage) during the lifetime of the animal. Extending lactation is a straight forward management practice in high-input dairy systems where a consistent supply of feed supplements is readily available, but may be more challenging to implement in low(er)-input pasture-based systems. The latter are much more seasonal, with a 12-month calving interval allowing pasture growth and quality to match the cow's nutritional demands; cows calve in spring when high-quality pasture is abundant and are dried-off during winter when pasture growth is more limited. In this review, we explored the impact of EL in both high-input systems and pasture-based systems. It covers the effects of EL on milk production, composition and processing, as well as on reproductive performance, health and welfare, and environmental and economic outcomes. [ABSTRACT FROM AUTHOR]

Streptococcus uberis is the most common cause of clinical mastitis at calving in pasture-based dairy cows. Results of experimental inoculations were compared with cows' previous history of infection to help define a model for susceptibility to Str. uberis mastitis. Cows used had either no apparent history of intramammary infection (IMI) by Str. uberis or other major mastitis pathogens throughout their productive lifetime (‘apparently uninfected’; AUI), or had a confirmed history of Str. uberis IMI (‘historically infected’; HI). Cows were exposed to Str. uberis in sequential steps: dipping of the teat end (DIP; n=53 cows); a teat canal inoculation (TCI; n=33 cows); and, finally, intramammary inoculation challenge (IC; n=7 cows). Only cows that remained free of infection at each step progressed to the next phase. Infection rates were similar between AUI or HI cows following the DIP (9 and 17% respectively), or the TCI (75 and 68% respectively). Physical and biochemical traits of cows were examined. Analysis of traits prior to inoculations implied that HI cows produced more milk fat, while AUI cows tended to have longer teat canals. Analysis of traits for cows that became infected following DIP, implied that there was a positive association with milk fat production and negative association with somatic cell count (SCC), while there was a positive association with the duration of p.m. milking, and negative association with SCC in those cows that became infected following TCI. Only AUI cows became infected following the IC inoculation. Similarity in response to experimental inoculation between the two groups suggests that the current dip or teat canal inoculation (using a 3-mm depth of inoculation) models are not good predictors of natural resistance to Str. uberis. However, a population of cows was identified that remained uninfected after DIP, TCI and IC, and may comprise a resistant phenotype. [ABSTRACT FROM PUBLISHER]

Abstract: Heifers managed under pastoral conditions are at risk from Streptococcus uberis mastitis infections at calving. A total of 397 heifers from six farms around New Zealand were enrolled in a study to identify and enumerate S. uberis on teat-ends of heifers in the peri-partum period, and to understand the effect of teat-spraying in the pre-calving period on the prevalence and incidence of S. uberis mastitis post-calving. Heifers were randomly assigned to Control or Sprayed groups. Sprayed heifers were teat-sprayed once, three times a week (Monday, Wednesday and Friday) with a commercial iodine-based teat sanitizer, starting at 3 weeks prior to calving and ending at day of calving. Across three farms, all glands of cows in both groups were sampled at calving to determine S. uberis intra-mammary infection (IMI) prevalence. For all farms, clinical mastitis (CM) cases detected during the week after calving were sampled and submitted for bacteriological analysis. Swabbing of teat-ends of 54 heifers from one farm showed that heifers had a pre-existing S. uberis contamination averaging 610 colony-forming units per swab (cfu/swab), at 3 weeks prior to calving. At calving, teat-end contamination was 560cfu/swab for Sprayed heifers and 1775cfu/swab for Control heifers. Two weeks after calving, teat-end contamination was similar between both groups, at 30cfu/swab. The prevalence of S. uberis IMI was significantly lower in the Sprayed (3.5% glands) vs. the Control (7.4%) heifers in the first week after calving. There was a trend for Sprayed heifers (3.6% heifers) to have a lower incidence of S. uberis CM compared with Control heifers (7.4% heifers). It is concluded that teat-spraying in the dry period is a management option that could contribute to controlling heifer S. uberis mastitis in the transition period. [Copyright &y& Elsevier]