Seasonality continues to receive more consideration by Missouri’s dairy producers. Although few are totally seasonal (calving all cows within a two month window), most are concentrating calving in the spring and fall seasons. Seasonal breeding and calving has both advantages and disadvantages compared to year-round calving.

Seasonal dairying allows producers to focus management efforts and tasks over specific time periods since all cows would be in a similar stage of production. The need for grouping cows by stage of lactation is essentially eliminated since all cows are dry at the same time, all cows freshen within about a 2 month period, all cows reach peak lactation at a similar time, and so on. Efforts could then be focused entirely on whatever stage the herd is at rather than having cows at different stages all the time. Issues such as calving, bottle feeding calves, estrus synchronization and heat detection are intense for a period of time, but then are done with for the remainder of the year.

Conversely, the advantages of seasonal dairying can be disadvantages to some producers. Management, labor and facilities must have the capacity to effectively handle these intensified tasks. Calving and bottle feeding an entire herd’s calf crop at one time requires more facilities and labor than needed for a non-seasonal dairy where there may only be a handful of calves at any given time. Synchronizing and AI-ing the entire herd at once requires a great deal of vigilance and endurance on the part of those doing the breeding. Having all cows dry for 45 to 60 days may create cash flow problems for individuals who have not adequately planned for 2 months without a milk check.

The SW Center dairy is totally seasonal, with the majority of cows freshening in February and March, and a few into early April. A spring calving herd matches the nutritional needs of the cows to the seasonal quality and availability of forages (pasture) better than calving in any other season. Although some justification can be made for fall calving (higher milk price in fall, cooler temperatures when breeding in November and December), much of the benefit of fall calving may be lost through the higher costs associated with feeding lactating cows through the winter months. Although heat stress can be an issue from June thru August for the spring calving dairy, various management strategies can be implemented to lessen the impact on milk production and reproduction.

Reproductive efficiency is always an important issue with a dairy operation, but even more so with a seasonal dairy. Heat (estrus) detection is one of the greatest challenges facing the dairyman. If cows are not bred in a timely manner, their calving will fall "outside the window" thus shortening their lactation and making it unlikely that they will breed back in time for the following year. Culling and replacing these otherwise sound cows because they are not bred or are bred too late is costly and reduces the overall profitability of the dairy.

Beginning in 2002, the SWC dairy has been comparing two different methods of heat detection. These included 1) visual observation combined with a visual detection aid, and 2) an electronic heat detection system. Each year, cows in the herd are randomly assigned to either group based on lactation number, days in milk, milk production and breed.

Cows in the visual detection group were observed for signs of estrus by a trained individual twice daily for 20-30 minutes. Cows were also fitted with a visual detection aid, either a K-mar® (during 2002 and 2003) or Estrus Alert® (2004) patch. The K-mar® device is a 2-3 inch long plastic vial filled with red dye within a white canvas-like patch which is glued to the tail head of the cow. When direct, continuous pressure from a mounting cow or bull is applied, the dye within the cylinder "bleeds" through a capillary opening causing the patch to change from white to bright red. The Estrus Alert ® patch is similar to a scratch-off ticket. Friction from mounting activity rubs off the silver coating to reveal a bright colored patch underneath.

Those cows first visually observed in standing heat in the morning were bred (AI) that same day late in the afternoon. Those not in heat in the morning, but first observed in standing heat in the afternoon were bred the following morning. Cows not seen standing, but with a red detection patch were bred at the next scheduled breeding time (am or pm) after detecting the red patch.

The second method of heat detection utilized the electronic HeatWatch® system. An electronic transmitter is activated with an individual cow’s ID, placed in a pouch on a large mesh patch, and glued to the tail head of the cow. When mounting pressure is applied to the transmitter, a signal is sent to a receiving antenna at the milking center. Cow ID, time of day and duration of mount are recorded in a buffer and downloaded to a computer allowing the producer to monitor cows 24 hours per day electronically. Since the time of first standing heat is known precisely, and timing of AI can be planned accordingly.

Heat detection and breeding began the first week of May and ended the middle of June. Following this, cows were exposed to a "clean up" bull. Ultrasonography was performed at 30-35 days post-AI to determine pregnancy. Please note that pregnancies resulting from the subsequent bull breeding are not included in the data below, only pregnancies from the AI period. Overall, the average number of AI services per conception was 1.91 in 2002, 1.75 in 2003, and 1.70 in 2004.

Preliminary data for the past three years indicate a slight numerical advantage in pregnancies for electronic system when compared to visual heat detection with visual aid (Table 1). Based on these limited data, approximately 75% (73 out of 97) of the cows were successfully bred by AI using the HeatWatch® system compared to 63% (62 out of 98) with visual observation combined with a visual patch.

What does this mean to the producer? Over the 3 years studied, there were 12 more cows (average of 4 per year) open following AI using the conventional heat detection method compared to HeatWatch®. The direct costs of having to replace those cows, as well as the indirect costs of loss of your genetic base and risk of bringing "problems" into the herd (disease, replacements with mastitis or blind quarters, genetically inferior animals) can contribute to reduced profitability.

The electronic heat detection system resulted in 11 more calves over 3 years compared to the conventional heat detection method. With a 50:50 sex ratio, that represents 5-6 more heifer calves or an average of about 2 per year. If one considers the recent price of a replacement heifer, this could represent several thousand dollars savings per year from reduced replacement costs (need to buy fewer heifers) or additional heifers that could be sold. The extra bull calves can also be an additional source of income.

The cost of the visual patches, while considerably less than the HeatWatch® system, and the fact that the latter is re-usable compared to the single use patch must also be factored in. Finally, the time and labor saved by using electronic heat detection compared to visual observation twice a day should be considered.

Reproductive efficiency research requires large numbers of observations over time. Additional data will continue to be collected over the upcoming years to better evaluate the cost effectiveness, as well as time and labor required, of the HeatWatch® system when compared to more traditional heat detection methods.