Stocking density during the transition period can be a critical factor determining whether or not a cow obtains sufficient intake and an adequate space at calving, which can affect production, behavior, stress response, and health. During the late dry period, adequate space has been associated with increased milk production and lower somatic cell count. As pre fersh stocking density in a free stall pen increased by 10%, above 80%, milk production decreased by 0.7 kg/d.49 Overstocking may have different impacts, however, based on environment and feeding system. For example, Proudfoot and colleagues50 observed cows stocked at 100% on an individual dual feeder versus those stocked at 150% did not differ in milk production. Although ensuring sufficient lying and eating space may decrease the likelihood of postpartum metabolic disease and milk production losses, environmental and housing factors may play a substantial role in understanding the effects of overstocking.
Lying time varies as cow's approach calving day, regardless of stocking density. Cows at 80% stocking density in free stalls spent more time lying on days 0, 5, and 7 before calving compared with cows stocked at 100%. Proudfoot and colleagues50 observed that multiparous cows in a competitive feeding environment spent 150 min/d less lying than cows feeding in a noncompetitive manner. These investigators noted that multiparous cows in competition for feeding space spent more time standing during the week before calving, 1 week pre partum, and 2.8 hours more during week 1 postpartum.
Understanding stocking density's relationship with feed bunk usage is important for providing adequate feed bunk space for sufficient dry matter intake and reduced aggression, particularly during the transition period. Pre partum mean meal time was 10 minutes per meal longer than postpartum. suggesting pre partum cows may need longer to break down a typical dry cow ration targeted at promoting rumen fill. Yet, among dry multiparous cows fed fresh feed once daily, only 65% to 69% visited the feed bunk at the time feed was delivered. Additionally, Huzzey and colleagues observed cows stocked at 150% in the freestalls and at the feed bunk took 30 minutes longer to approach the feed bunk after fresh feed delivery compared with those stocked at 100%. Cows not able to eat freshly delivered feed ate 14% less, leading to decreased dry matter intake and increased disease incidence postpartum. Providing sufficient feed bunk space is necessary for allowing cows to eat longer and receive fresh feed immediately after delivery.
Across multiple studies, there is a strange dynamic with dry matter intake and stocking density. Prepartum cows in overstocked pens consistently consume more feed per head than those at 100% stocking density. Dry matter intake was 1 kg/cow/d more among cows stocked at 150% than those at 100% stocking den- sity,54,55 suggesting a greater feeding rate and potential for slug feeding and ruminal digestion problems. 56 Feed consumption per cow stocked at 4 cows per individual feeder was 25% more than calculated requirements. 57,58 These cows also spent 4% less time eating.
Stocking density should be evaluated as a means of reducing negative social interactions between cows,1 because displacements can decrease a cow's ability to meet dietary needs. Feeding behavior may be more affected by stocking density in primiparous cows, because limited resources are a greater challenge to this group. Multiparous cows had a greater social dominance score than primiparous cows when housed together.59 Among cows that shared an Insentec feeder (Marknesse, the Netherlands), primiparous cows were replaced 25 times/d in a competition situation compared with 7 times
d in a noncompetitive situation.50 In mixed housing, without individually assigned feeding space, as seen among traditionally housed cows, primiparous cows may be displaced with a greater frequency when over- stocked than when stocked at 100%. Lobeck-Luchterhand and colleagues52 observed that despite multiparous cows spending 47 min/d more feeding than nulliparous cows, no variation in social ranking was observed. Additionally, Proudfoot and colleagues50 reported no difference in feeding time, frequency of visits to a feeder, dry matter intake per visit, or total daily feeding time among cows stocked at 100% or 150%. Further work must be proposed to explore the development of social hierarchy and the role of feeding behavior among dry cows, considering parity as a confounding factor.
Varying stocking density can have an impact on number of displacements from the feed bunk or feeding space, regardless of parity. Huzzey and colleagues 55 observed 22 more displacements from the feed bunk per day among cows housed at 150% versus those housed at 100% When 1 cows shared a single automatic feeder dis.
versus those housed at 100%. When 4 cows shared a single automatic feeder, dis- placements were 38% greater than when an individual cow was assigned an individual automatic feeder. Dry cows stocked at 80% had 6 less displacements from the feed bunk per day than cows stocked at 100% stocking density.52 This suggests that regardless of stocking density, some low level of displacements occur within any given system.
Use of corticotropin has become a common way to assess dry cow stress associated with increased stocking density. Results can vary greatly, however, due to confound- ing variables within studies. Elevated fecal cortisol metabolite, plasma nonesterified fatty acids, and glucose concentration were greater among cows stocked at 150% versus cows housed at 100%.55 Furthermore, low ranked cows administered a glucose tolerance test, had a greater insulin response and tended to have greater nonesterified fatty acid response than the high ranked cows. 54 Determining the effects of stocking density on dry cows must be further explored, considering a range of stocking densities from 80% to 200%, to provide a more representative sample of management practices. Although stocking density and management style can vary greatly within a single dry cow group, providing better guidelines for how to manage dry cows in all systems is necessary to promote dairy cow health and decrease stress postpartum.