*Rick Grant is president of the William H. Miner Agricultural Research Institute in Chazy, N.Y.

FREESTALL and feed bunk overstocking is commonplace in the U.S. dairy industry.

The U.S. Department of Agriculture's National Animal Health Monitoring System reported that 58% of dairy farms provide less than the recommended 24 in. of bunk space per cow, and 43% provided less than one stall per cow (2010 data).

Another study found that 78% of farms in the northeastern U.S. had feed bunk stocking densities in excess of 100% (von Keyserlingk et al., 2012).

Overstocking may improve economic returns on facility investments, but it also compromises the cow's ability to practice natural behaviors, which is a primary factor related to well-being.

Reduced performance

In one study in which 47 dairy herds had similar nutrition and genetics, freestall stocking density alone explained 32% of the variation in milk production among the farms (Bach et al., 2008).

As stocking density increases, herds experience a reduced average milk yield. De Vries et al. (2016) recently reviewed the literature and found that, for each 10-percentage unit increase in stall stocking density, cows averaged 0.76 lb. per day less milk, and the probability of conception declined by 10 percentage units.

Higher stocking density consistently reduces feeding time and boosts aggression at the feed bunk (Huzzey et al., 2006). It also drives greater rates of feed consumption — up to 25% faster — and larger meal sizes (Hill et al., 2009; Collings et al., 2011).

In addition to undesirable feeding behavior, overstocking also compromises lying time and suppresses recumbent rumination activity (Fregonesi et al., 2007; Krawczel et al., 2012).

Caraviello et al. (2006) identified the factors of greatest importance to influencing reproductive performance. Bunk space in the breeding pen topped the list of factors. These researchers found that as bunk space decreased from 24 in. to 12 in. per cow, the percentage of cows pregnant by 150 days in milk decreased from 70% to 35%.

Similarly, Schefers et al. (2010) observed reduced conception rates with higher stocking densities.

Economics of overstocking

Although overstocking perturbs natural cow behavior and reduces performance, it can improve economic returns on facility investments. Recently, researchers in Florida and the Netherlands modeled the economics of varying the stall stocking density between 100% and 150% on profits per stall (De Vries et al., 2016).

They especially focused on milk yield, the probability of conception and the probability of culling as a function of stocking density. Factors external to the farm were also incorporated into their model, such as feed and milk prices.

The optimal stall stocking density for any combination of inputs was most sensitive to: (1) potential milk production loss as a result of overstocking, (2) the cost of feed and (3) milk prices.

With their model, these researchers were able to evaluate more than 2,000 input combinations and found that, for all of those scenarios, a stall stocking density of about 120% was optimal, with an annual average maximum increase in profit of $99 per stall.

The law of diminishing returns governs the economics of stall stocking density (De Vries et al., 2016). Each additional cow added to a pen generates additional revenue, but it also comes with variable costs, such as feed, supplies and labor. Based on published data, it is also known that incrementally adding cows will — beyond a certain point that varies from herd to herd — reduce the performance of the other cows within the pen.

According to the model created by De Vries et al. (2016) the economic optimum for stocking density occurs when the marginal returns of the pen equal the marginal costs of the pen.

Overstocking dilemma

An overstocking dilemma arises because the optimal economic return may not always coincide with optimal cow well-being (Grant, 2016). For example, it is known that resting is the behavior most highly valued by the cow and is a significant component of the cow's well-being (Munksgaard et al., 2005).

Some studies have found that lying time decreases with any level of stall stocking that exceeds 100% (Fregonesi et al., 2007). Based on these data, stocking freestalls to 120% to optimize economic returns presents a dilemma: choosing between economics and cow well-being. On the other hand, considerable variation exists in the reported literature on resting response to stocking density between 100% and 120%. However, the bottom line conclusion is that, beyond 120% stall stocking density, all studies show a reduction in the cows' lying time.

It can be concluded that optimal profit per stall and cow well-being are both achievable under ideal management conditions. The model of De Vries et al. (2016) will help identify the economically optimum stocking density for any specific set of on-farm circumstances. However, the dairy industry must recognize that, for some farms, a trade-off will occur between economics and well-being. That is a critical dilemma the industry must confront.

The Bottom Line

The economic impact of overcrowding encompasses depressed health, reproduction and milk yield. Stocking stalls and feed bunk space at approximately 120% appears to be a critical point beyond which a trade-off between economics and well-being becomes increasingly likely.

A recently published model allows users to assess optimal stall stocking density under varying economic conditions, and readers are encouraged to access it online from the Journal of Dairy Science.

References

Bach, A., N. Valls, A. Solans and T. Torrent. 2008. Associations between non-dietary factors and dairy herd performance. J. Dairy Sci. 91:3259-3267.

Caraviello, D.Z., K.A. Weigel, P.M. Fricke, M.C. Wiltbank, M.J. Florent, N.B. Cook, K.V. Nordlund, N.R. Zwald and C.L. Rawson. 2006. Survey of management practices on reproductive performance of dairy cattle on large U.S. commercial farms. J. Dairy Sci. 89:4723-4735.

Collings, L.K.M., D.M. Weary, N. Chapinal and M.A.G. von Keyserlingk. 2011. Temporal feed restriction and overstocking increase competition for feed by dairy cattle. J. Dairy Sci. 94:5480-5486.

De Vries, A., H. Dechassa and H. Hogeveen. 2016. Economic evaluation of stall stocking density of lactating dairy cows. J. Dairy Sci. 3848-3857.

Fregonesi, J.A., C.B. Tucker and D.M. Weary. 2007. Overstocking reduces lying time in dairy cows. J. Dairy Sci. 90:3349-3354.

Grant, R.J. 2016. The overstocking dilemma. The William H. Miner Agricultural Research Institute Farm Report, pp. 1 and 11. Chazy, N.Y. Accessed at: http://whminer.org/dairy/farm-report.php.

Huzzey, J.M., T.J. De Vries, P. Valois and M.A.G. von Keyserlingk. 2006. Stocking density and feed barrier design affect the feeding and social behavior of dairy cattle. J. Dairy Sci. 89:126-133.

Krawczel, P.D., C.S. Mooney, H.M. Dann, M.P. Carter, R.E. Butzler, C.S. Ballard and R.J. Grant. Effect of alternative models for increasing stocking density on the short-term behavior and hygiene of Holstein dairy cows. 2012. J. Dairy Sci. 95:2467-2475.

Munksgaard, L., M.B. Jensen, L.J. Pedersen, S.W. Hansen and L. Matthews. 2005. Quantifying behavioral priorities — Effects of time constraints on behavior of dairy cows, Bos Taurus. Appl. Anim. Behav. Sci. 92:3-14.

Schefers, J.M., K.A. Weigel, C.L. Rawson, N.R. Zwald and N.B. Cook. 2010. Management practices associated with conception rate and service rate of lactating Holstein cows in large, commercial dairies. J. Dairy Sci. 93:1459-1467.

U.S. Department of Agriculture. 2010. Facility characteristics and cow comfort on U.S. dairy operations, 2007. Animal & Plant Health Inspection Service-Veterinary Services, Cent. Epidemiol. Anim. Health, Ft. Collins, Colo.

Von Keyserlingk, M.A.G., A. Barrientos, K. Ito, E. Galo and D.M. Weary. 2012. Benchmarking cow comfort on North American freestall dairies: lameness, leg injuries, lying time, facility design and management for high-producing Holstein dairy cows. J. Dairy Sci. 95:1-10.

Volume:88 Issue:08